After seeing active service in the Second World War, enlisting in the Royal Engineers in 1941 and later being commissioned and reaching the rank of Captain, Gunter entered Parliament in the 1945 general election for the previously Conservative seat of South East Essex.
But even at that election he won his seat by a majority of only 878 over his Conservative opponent, Anthony Barber (future cabinet minister).
Barber went on to unseat Gunter by 384 votes in the 1951 general election that saw the return of a Conservative Government under Winston Churchill.
When George Isaacs (aged 76) announced his decision not to stand for re-election in the strongly Labour constituency of Southwark in South London, Gunter secured the nomination in time for the 1959 general election.
Gunter was re-elected in his Southwark constituency at the 1970 general election that saw the Labour government replaced by a Conservative one led by Edward Heath.