[2]: 4 [3][4] His correspondence from his time at Princeton showed his deep dismay over the rise of McCarthyism and the election of Dwight D. Eisenhower as president.

[2]: 4–6  He was elected Member of Parliament for Berwick and East Lothian in 1966, as Labour won a landslide victory nationwide.

[3] Later in life, Mackintosh became chair and professor of politics at the University of Edinburgh, where he managed to balance his duties in the House of Commons with teaching students, a role he enjoyed.

While in Ibadan, Mackintosh met Una Maclean, a doctor and anthropologist; they married in 1963, the same year his first marriage was dissolved.

[6] In the ensuing by-election to the Berwick and East Lothian constituency, his seat was won by John Home Robertson.

[7] Dewar himself, when First Minister of Scotland, said of John Mackintosh's lifelong belief in devolution: "His ideas had a lasting influence.

....[He] was a powerful advocate for devolution...John was something of a prophet, a mighty champion of reform at a time when constitutional change was not an approved and certainly not a fashionable cause.

His vision was good government, an equitable democracy, that borrowed, elevated, created opportunity for the citizen."

A memorial lecture was founded by Arthur Greenan, his friends in the constituency and colleagues in Edinburgh University.