Bowdoin as named as a delegate to the First Continental Congress in 1774 but did not attend, citing the poor health of his wife. A bout of poor health, probably caused by tuberculosis, at the time also affected him. Bowdoin was again ill in 1775 when the American Revolutionary War broke out, and the family was relocated from British-occupied Boston (which was then under siege by area militia) first to Dorchester, and eventually to Middleborough, where he resided until 1778. (Bowdoin's Beacon Street mansion was occupied by General John Burgoyne.) Despite his convalescence he was kept apprised of events occurring in and around Boston, and was elected president of the executive council of the Massachusetts Provincial Congress. This position, which he held until 1777, made him the "de facto" head of the Massachusetts government. Citing his ongoing poor health, he resigned the post and withdrew from public view. He continued to correspond with other revolutionaries, and enjoyed their confidence, although his absence from the war effort would lead to later political difficulties. He began to return to public life in 1778, and when Massachusetts wrote its own constitution in 1779, he was president of the convention called to create it, and chairman of the committee that drafted it. John Adams, also a committee member, is generally credited as the major author of the new constitution, although Bowdoin and Samuel Adams likely made significant contributions.