The patriot blood spilled at Lexington and Concord fired a martial spirit throughout America by which the bold leaders in every State were nerved to resist and resent those unprovoked assaults, and when Washington appeared at the camp in Boston as the Commander-in-Chief of the American armies, Mifflin was by his side.
Recognizing his great personal popularity, the ease and dignity of his manners, breadth and soundness of his views, Washington placed Mifflin at the head of his military family. In the absence of, or at the retirement from the table of the chief it fell upon Mifflin to occupy his place and do the honors; and for this duty, by his social position at home and his foreign travel he was admirably fitted. Colonel Mifflin was the first person in America who officiated as aide-de-camp.
When Washington, July, 1775, organized the entire army, the difficult position of quartermaster general was assigned to Mifflin. The duties were new and arduous. Everything was in chaos. Order had to be established and system inaugurated.
On May 19, 1776, Congress appointed and commissioned Mifflin to be a brigadier general and he was given command of Pennsylvania troops. An assignment to the active field was much more to his liking than one at headquarters.
Upon taking the field Mifflin was relieved as quartermaster general by General Stephen Moylan, who was ill suited to the difficult task of providing for an army where the authority for calling in supplies was little respected and the means of paying for them was rarely in hand; and not long after accepting the position he abandoned it.
Congress called upon Mifflin to again assume the duties of quartermaster general and he reluctantly responded to the call of his country, deeming it a matter of duty.
The reverses of the American Army during the summer and fall of 1776 culminated in its withdrawal into New Jersey, hotly pursued by the British troops. Pennsylvania was threatened and especially Philadelphia, where Congress was sitting. At this dark hour Mifflin was sent with dispatches from Washington to Congress, calling on that body loudly for help.
Mifflin, at the request of Congress, made a stirring address, setting forth the perilous situation, and appealing for the means to oppose the further advance of the defiant enemy. That body was greatly exercised and ordered that General Mifflin should remain near Congress for consultation and advice.
As the enemy pressed toward Philadelphia, General Putnam was sent to take command in the city and General Mifflin was placed in charge of the war material and stores.
The victory at Trenton produced a gleam of hope and Congress dispatched Mifflin throughout the State of Pennsylvania in order that, by his personal appeals, volunteers might be drawn to the support of Washington’s decimated ranks. He caused large numbers to enlist.