Ainsley attended elementary school before enlisting in the Durham Light Infantry in 1916 to fight in the First World War.
In 1942 he was appointed to Durham County Council (elections having been suspended during the war), where he specialised in education and became Chairman of the Education Committee; served on the council until 1956, including a term as Chair from 1953 to 1955, and as Alderman the following year.
[1] In December 1950 he was part of a delegation to central government over Durham County Council's decision to institute a closed shop for all its employees.
For the 1955 general election, Ainsley was selected as Labour Party candidate for North West Durham.
He was generally loyal to the Labour Party (never breaking the whip), and when asked in 1959, he withdrew his name from a motion which opposed any move of NATO aircraft from French to British bases.