From the time of his leaving school till the latter part of 1753, Washington was unconsciously preparing himself for the great duties he had afterward to discharge. An attempt made to have him entered in the Royal Navy, in 1746, was frustrated by the interposition of his mother. The winter of 1748-49 he passed at Mount Vernon, then the seat of his brother Lawrence, in the study of mathematics and the exercise of practical surveying. George was introduced about this time to the family of Lord Fairfax, his brother having married the daughter of William Fairfax, a member of the Colonial Council, and a distant relative of that nobleman. The immense tracts of wild lands belonging to Lord Fairfax, in the valley of the Alleghany Mountains, had never been surveyed; he had formed a favorable estimate of the talents of young Washington, and intrusted the task to him. His first essay was on some lands situated on the south branch of the Potomac, seventy miles above its junction with the main branch. Although performed in an almost impenetrable country, while winter yet lingered in the valleys, by a youth who had only a month before completed his sixteenth year, it gave so much satisfaction that he soon after received a commission as public surveyor, an appointment which gave authority to his surveys, and enabled him to enter them in the county offices.

The next three years were devoted without intermission, except in the winter months, to his profession. There were few surveyors in Virginia, and the demand for their services was consequently great, and their remuneration ample. Washington spent a considerable portion of these three years among the Alleghanies. The exposures and hardships of the wilderness could be endured only for a few weeks together, and he recruited his strength by surveying, at intervals, tracts and farms in the settled districts. Even at that early age his regular habits enabled him to acquire some property; and his probity and business talent obtained for him the confidence of the leading men of the colony.

At the time he attained his nineteenth year the frontiers were threatened with Indian depredations and French encroachments. To meet this danger the province was divided into military districts, to each of which an adjutant-general with the rank of major was appointed. George Washington was commissioned to one of these districts, with a salary of £150 per annum. There were many provincial officers (his brother among the number) in Virginia, who had served in the expedition against Carthagena and in the West Indies. Under them he studied military exercises and tactics, entering with alacrity and zeal into the duties of his office. These pursuits were varied by a voyage to Barbadoes, and a residence of some months in that colony, in company with his brother Lawrence, who was sent there by his physicians to seek relief from a pulmonary complaint. Fragments of the journal kept by George Washington on this excursion have been preserved; they evince an interest in a wide range of subjects, and habits of minute observation. At sea the log-book was daily copied, and the application of his favorite mathematics to navigation studied; in the island, the soil, agricultural products, modes of culture, fruits, commerce, military force, fortifications, manners of the inhabitants, municipal regulations and government, all were noted in this journal. Lawrence Washington died in July, 1752, leaving a wife and infant daughter, and upon George, although the youngest executor, devolved the whole management of the property, in which he had a residuary interest. The affairs of the estate were extensive and complicated, and engrossed much of his time and thoughts for several months. His public duties were not, however, neglected. Soon after the arrival of Governor Dinwiddie the number of military divisions was reduced to four and the northern division allotted to Washington. It included several counties, which he had visited at stated intervals, to train and instruct the military officers, inspect the men, arms, and accoutrements, and establish a uniform system of manœuvres and discipline.

In 1753 the French in Canada pushed troops across the lakes, and at the same time bodies of armed men ascended from New Orleans to form a junction with them, and establish themselves on the upper waters of the Ohio. Governor Dinwiddie resolved to send a commissioner to confer with the French officer in command, and inquire by what authority he occupied a territory claimed by the British. This charge required a man of discretion, accustomed to travel in the woods, and familiar with Indian manners. Washington was selected, notwithstanding his youth, as possessed of these requisites. He set out from Williamsburg on October 31, 1753, and returned on January 16, 1754. He discovered that a permanent settlement was contemplated by the French within the British territory, and notwithstanding the vigilance of the garrison, he contrived to bring back with him a plan of their fort on a branch of French Creek, fifteen miles south of Lake Erie, and an accurate description of its form, size, construction, cannon, and barracks.

In March, 1754, the military establishment of the colony was increased to six companies. Colonel Fry, an Englishman of scientific acquirements and gentlemanly manners, was placed at the head of them, and Washington was appointed second in command. His first campaign was a trying but useful school to him. He was pushed forward, with three small companies, to occupy the outposts of the Ohio, in front of a superior French force, and unsupported by his commanding officer. Relying upon his own resources and the friendship of the Indians, Washington pushed boldly on. On May 27th he encountered and defeated a detachment of the French army under M. De Jumonville, who fell in the action. Soon after Colonel Fry died suddenly, and the chief command devolved upon Washington. Innis, the commander of the North Carolina troops, was, it is true, placed over his head, but the new commander never took the field. An ill-timed parsimony had occasioned disgust among the soldiers, but Washington remained unshaken. Anticipating that a strong detachment would be sent against him from Fort Duquesne as soon as Jumonville's defeat was known there, he intrenched himself on the Great Meadows. The advance of the French in force obliged him to retreat, but this operation he performed in a manner that elicited a vote of thanks from the House of Burgesses. In 1755 Colonel Washington acceded to the request of General Braddock to take part in the campaign as one of his military family, retaining his former rank. When privately consulted by Braddock, "I urged him," wrote Washington, "in the warmest terms I was able, to push forward, if he even did it with a small but chosen band, with such artillery and light stores as were necessary, leaving the heavy artillery and baggage to follow with the rear division by slow and easy marches." This advice prevailed. Washington was, however, attacked by a violent fever, in consequence of which he was only able to rejoin the army on the evening before the battle of the Monongahela. In that fatal affair he exposed himself with the most reckless bravery, and when the soldiers were finally put to rout, hastened to the rear division to order up horses and wagons for the wounded. The panic-stricken army dispersed on all sides, and Washington retired to Mount Vernon, which had now, by the death of his brother's daughter without issue, become his own property. His bravery was universally admitted, and it was known that latterly his prudent counsels had been disregarded.

In the autumn of the same year he was appointed to reorganize the provincial troops. He retained the command of them till the close of the campaign of 1758. The tardiness and irresolution of provincial assemblies and governors compelled him to act during much of this time upon the defensive; but to the necessity hence imposed upon him of projecting a chain of defensive forts for the Ohio frontier, he was indebted for that mastery of this kind of war, which afterward availed him so much. Till 1758 the Virginia troops remained on the footing of militia; and Washington having had ample opportunities to convince himself of the utter worthlessness of a militia in time of war, in the beginning of that year prevailed upon the Government to organize them on the same footing as the royal forces. At the same time that Washington's experience was extending, his sentiments of allegiance were weakened by the reluctance with which the claims of the provincial officers were admitted, and the unreserved preference uniformly given to the officers of the regular army. At the close of 1758 he resigned his commission and retired into private life.

On January 6, 1759, he married Mrs. Martha Custis, a young widow with two children. "Mr. Custis," says Mr. Sparke, "had left large landed estates, and £45,000 sterling in money. One-third of this property she held in her own right; the other two-thirds being equally divided between her two children." Washington had a considerable fortune of his own at the time of his marriage, consisting of the estate at Mount Vernon, and large tracts of land which he had selected during his surveying expeditions and obtained grants of at different times. He now devoted himself to the management of this extensive property, and to the guardianship of Mrs. Washington's children, and till the commencement of 1763 was, in appearance at least, principally occupied with these private matters. He found time, however, for public civil duties. He had been elected a member of the House of Burgesses before he resigned his commission, and although there were commonly two, and sometimes three sessions in every year, he was punctual in his attendance from beginning to end of each. During the period of his service in the Legislature he frequently attended on such theatrical exhibitions as were then presented in America, and lived on terms of intimacy with the most eminent men of Virginia. At Mount Vernon he practised on a large scale the hospitality for which the Southern planters have ever been distinguished. His chief diversion in the country was the chase. He exported the produce of his estates to London, Liverpool, and Bristol, and imported everything required for his property, and domestic establishment. His industry was equal to his enterprise; his day-books, ledgers and letter-books were all kept by himself and he drew up his own contracts and deeds. In the House of Burgesses he seldom spoke, but nothing escaped his notice, and his opinion was eagerly sought and followed. He assumed trusts at the solicitation of friends, and was much in request as an arbitrator. He was, probably without being himself aware of it, establishing a wide and strong influence, which no person suspected till the time arrived for exercising it.

On March 4, 1773, Lord Dunmore prorogued the intractable House of Burgesses. Washington had been a close observer of every previous movement in his country, though it was not in his nature to play the agitator. He had expressed his disapprobation of the Stamp Act in unqualified terms. The non-importation agreement, drawn up by George Mason in 1769, was presented to the members of the dissolved House of Burgesses by Washington. In 1773 he supported the resolutions instituting a committee of correspondence and recommending the legislatures of the other colonies to do the same. He represented Fairfax County in the Convention which met at Williamsburg, in August, 1774, and was appointed by it one of the six Virginian delegates to the first General Congress. On his return from Congress he was virtually placed in command of the Virginian Independent Companies. In the spring of 1775 he devised a plan for the more complete military organization of Virginia; and on June 15th of that year, he was elected commander-in-chief of the continental army by Congress.