When Bonaparte returned to Paris Marmont accompanied him, and was offered the post of superintendent of the gun factory at Moulins. He contemptuously refused this position, telling the inspector of ordnance that he would not mind such a post in peace time, but that he was going to see as much active service as he could while the war lasted, so at his own request he was posted to the army of Pichegru, which was besieging Maintz.
A temporary suspension of hostilities on the Rhine gave him the opportunity of once again joining his chosen leader, and early in 1796 he started for Italy on Bonaparte's staff. Lodi was one of the great days of his life. Early in the action he captured one of the enemy's batteries, but a moment later he was thrown from his horse and ridden over by the whole of the cavalry, without, however, receiving a single scratch. Scarcely had he mounted when he was despatched along the river, under fire of the whole Austrian force on the other bank, to carry orders to the commander of the cavalry, who was engaged in fording the river higher up. Of his escort of five, two were killed, while his horse was severely wounded, yet he managed to return in time to take his place among the band of heroes who forced the long bridge in the face of a storm of bullets and grape. Castiglione added to his laurels, for it was his handling of the artillery that enabled Augereau to win his great victory. The Marshal, in his Memoirs, asserts that this short campaign was the severest strain he ever underwent. "I never at any other time endured such fatigue as during the eight days of that campaign. Always on horseback, on reconnaissance, or fighting, I was, I believe, five days without sleep, save for a few stolen minutes. After the final battle the general-in-chief gave me leave to rest and I took full advantage of it. I ate, I lay down, and I slept twenty-four hours at a stretch, and, thanks to youth, hardiness, a good constitution, and the restorative powers of sleep, I was as fresh again as at the beginning of the campaign."
Though Castiglione thus brought him fresh honours, it nearly caused an estrangement between him and his chief. For Bonaparte, ever with an eye to the future, desiring to gain as many friends as possible, chose one of Berthier's staff officers to take the news of the victory to Paris. This was a bitter blow to his ambitious aide-de-camp, whose pride was further piqued because his hero, forgetting that he had not to deal with one of the ordinary adventurers who formed so large a number of the officers of the Army of Italy, with great want of tact, had offered him opportunities of adding to his wealth by perquisites and commissions abhorrent to the eyes of a descendant of an honourable family. But the exigencies of war and the thirst for glory left little time for brooding, and Bonaparte, recognising with whom he had to deal, took the opportunity of the successful fighting which penned Würmser into Mantua to send Marmont with despatches to Paris. As his reward the Minister of War promoted him colonel and commandant of the second regiment of horse artillery. A curious state of affairs arose from this appointment, for promotion in the artillery ran quite independent of ordinary army rank. Accordingly, the army list ran as follows: Bonaparte, lieutenant-colonel of a battalion of artillery, seconded as general-in-chief of the Army of Italy. Marmont, colonel of the second regiment horse artillery, seconded as aide-de-camp to Lieutenant-Colonel Bonaparte, the commander-in-chief of the Army of Italy.
Marmont hurried back to Italy in time to join Bonaparte's staff an hour before the battle of Arcola. The Austrians were making their last effort to relieve the fortress of Mantua, and it seemed as if they would be successful, as Alvinzi had concentrated forty thousand troops against twenty-six thousand. The French attempted a surprise, but were discovered, and for three days the fate of the campaign hung on the stubborn fight in the marshes of Arcola. It was Marmont who helped to extricate Bonaparte when he was flung off the embankment into the ditch, a service which Bonaparte never forgot. Diplomatic missions to Venice and the Vatican slightly turned the young soldier's head, and his chief had soon to give him a severe reprimand for loitering among Josephine's beauties at Milan instead of hastening back to headquarters. But to a man of Marmont's character one word of warning was enough; his head governed his heart; glory was his loadstar. Ambitious though he was, he was essentially a man of honour and fine feelings, and refused the hand of Pauline Bonaparte for the simple reason that he did not truly love her.
A year later he made a love match with Mademoiselle Perrégaux, but differences of temperament and the long separation which his military career imposed caused the marriage to turn out unhappily, and this lack of domestic felicity spoiled the Marshal's life and nearly embittered his whole character, turning him for the time into a self-centred man with an eye solely to his own glory and a sharp tongue which did not spare even his own friends. Yet in his early days Marmont was a bright and cheerful companion and no one enjoyed more a practical joke, getting up sham duels between cowards or sending bogus instructions to officious commanders. But fond as he was of amusement, even during his early career he could find delight in the society of men of science and learning like Monge and Berthollet.
After the peace of Campo Formio he accompanied his chief to Paris, where an incident occurred which illustrates well the character of the two men. The Minister of War wanted detailed information regarding the English preparations against invasion, and Bonaparte offered to send his aide-de-camp as a spy. Marmont indignantly refused to go in such a capacity, and a permanent estrangement nearly took place. Their standards had nothing in common; in the one honour could conquer ambition, in the other ambition knew no rules of honour.
However, their lust for glory brought them together again, and Marmont sailed with the Egyptian expedition. He was despatched north to command Alexandria after the battle of the Pyramids, where his guns had played so important a part in shattering the Mamelukes. Later he was entrusted with the control of the whole of the Mediterranean littoral. His task was a difficult one, but a most useful training for a young commander. With a tiny garrison he had to hold the important town of Alexandria and to keep in order a large province; to organise small columns to repress local risings; to make his own arrangements for raising money to pay his troops, and consequently to reorganise the fiscal system of the country; to reconstruct canals and to improvise flotillas of barges to supply Alexandria with provisions; to keep in touch with the remnant of the French fleet and thus to try to establish communications with Europe. He was responsible for resisting any attempt at invasion by the Turks or the English, and it was mainly owing to his measures that when the former landed at Aboukir they were destroyed before they could march inland. While his comrades were gaining military glory in Syria, he was fighting the plague at Alexandria, learning that patient attention to detail and careful supervision of the health of his troops were as important attributes of a commander as dash and courage in the field.
Marmont quitted Egypt with joy; he had learned many useful lessons, but, like the rest of the army, he hated the country and the half Oriental life, and above all, as he said, "seeing a campaign and not taking part in it was a horrible punishment." On returning to Paris his time was fully occupied in winning over the artillery to Bonaparte. He had no false ideas on the subject, for, as he said to Junot before the Egyptian expedition, "You will see, my friend, that on his return Bonaparte will seize the crown." As his reward the First Consul gave him the choice of the command of the artillery of the Guard or a seat as Councillor of State. Jealous of Lannes, and flattered by the title, he chose the councillorship, in which capacity he was employed on the War Committee and entrusted with the reorganisation of the artillery. His first business was to provide a proper train to ensure the quick and easy mobilisation of the artillery. After the Marengo campaign he took in hand the reform of the matériel. Too many different types of guns existed. Marmont reorganised both the field and the fortress artillery, replacing the seven old types of guns by three—namely, six-pounders, twelve-pounders and twenty-four pounders; he also reduced the different types of wheels for gun carriages, limbers and wagons from twenty-four to eight, thus greatly simplifying the provision of ammunition and the work of repair in the field.
The Marengo campaign added to his prestige as an artillery officer. It was owing to his ingenuity that the guns were unmounted and pulled by hand in cradles up the steep side of the mountain and thus safely taken over the St. Bernard Pass. It was his ingenious brain which suggested the paving of the road with straw, whereby the much-needed artillery was forwarded to Lannes by night, without any casualties, right under the batteries of the fortress of Bard. It was owing to his foresight that the reserve battery of guns, captured from the enemy, saved the day at Marengo by containing the Austrians while Desaix's fresh troops were being deployed, and it was the tremendous effect of his massed battery which gave Kellermann the opportunity for his celebrated charge. The First Consul marked his approval by promoting Marmont a general of division, and thus at the age of twenty-six the young artillery officer had nearly reached the head of his profession. After Marengo he continued his work of reorganisation, but before the end of the year he was once again in Italy, this time as a divisional commander under Brune, who, being no great strategist, was glad to avail himself of the brains of the First Consul's favourite: it was thanks to Marmont's plans that the French army successfully crossed the Mincio in the face of the enemy and, forced on him the armistice of Treviso. When Moreau's victory of Hohenlinden induced Austria to make peace, the general was sent to reorganise the Italian artillery on the same principles he had laid down for the French. He established an immense foundry and arsenal at Pavia, and the excellence of his plans was clearly proved in many a later campaign. From Italy he was recalled to Paris in September, 1802, as inspector-general of artillery. He threw himself heart and soul into his new duties, but found time to increase his scientific knowledge and to keep himself up to date with everything in the political and scientific world. He keenly supported Fulton's invention of the steamboat, and pressed it on the First Consul, and to the day of his death he was convinced that, if the Emperor had adopted the invention, the invasion of England would have been successful.