Heap served as a Member of Parliament with the New Democratic Party, a Toronto City Councillor, a political activist and an Anglican worker-priest.

[1] For his last two years of high school, Heap attended Upper Canada College on a scholarship, and then studied classics and philosophy at Queen's University.

[1] A pacifist, Heap nevertheless joined the Canadian Army during the Second World War due to his opposition to Nazism, later saying "It wasn't possible to be neutral in the face of Hitler".

[1] While at McGill he became engaged to Alice Boomhour, a pacifist, activist in the SCM and CCF, and daughter of a United Church minister.

[2] After working as a parish priest in Quebec for only a few years in the 1950s, Heap decided against a career as a church employee and aligned himself with the Worker-Priest movement which paired ministry with social activism.

[2] He and Alice raised seven children, including son Danny Heap, a computer science lecturer at the University of Toronto.

When the Liberal Member of Parliament for Spadina, Peter Stollery, was appointed to the Senate in 1981, Heap decided to run in the subsequent by-election.

[11] Despite retiring from politics, Heap remained involved as an activist, strongly backing the anti-war movement, and supporting NDP candidates in the region.

In 2011, he and his wife faced eviction from their retirement home as they awaited admission to a long-term care facility, for which they had been on a waiting list for five years.

[7][14] One of his sons posted a message remembering him as an "advocate of the homeless, for refugees and for peace [among other causes]" and also as a "Pacifist, socialist, worker-priest, marxist Anglican, trade-unionist, city councillor, member of parliament, civilly disobedient marcher for human rights.

In 2013, Nadira Fraser established the "Dan and Alice Heap Bursary" to aid single parents to qualify for nursing.