Winch was active during the relief camp strike in Vancouver that precipitated the On-to-Ottawa Trek in 1935, acting as a liaison between unemployed protesters and the government. He performed the same role as a new MLA in 1938, and assisted the police in ending a month-long occupation at the Vancouver Art Gallery on what became known as "Bloody Sunday".
Winch survived the 1958 federal election that almost wiped the CCF out, and remained with the party as it transformed into the New Democratic Party in 1961. After winning seven successive elections as an MP, he retired from the House of Commons at the 1972 federal election.
Harold Winch's father, Ernest Edward Winch was also a CCF MLA from 1933 until his death in 1957.