Macdonald was a close political and personal ally of President John F. Kennedy, his former roommate at Harvard College.

Macdonald attended Harvard University, where he was captain of the Crimson football team and the roommate of John F. Kennedy.

He was admitted to the bar in 1946 and commenced the practice of law in Boston as a partner in the firm of Stoneman, Macdonald & Chandler.

During his career, he served as majority Whip, and as ranking Democrat on the House Committee on Interstate and Foreign Commerce.

Another focus was his effort to reform campaign broadcasting practices, addressing his concern that competent candidates were being priced out of the process, and others were buying their way in.

While recognized as an active legislator, he was also justly noted for his high level of service to individual constituents and their problems.