Kershaw contested Gloucester in 1950 and 1951. He was elected as Member of Parliament (MP) for Stroud in 1955, remaining in that position until his retirement at the 1987 general election, with a substantially increased majority. He supported National Service in his maiden speech. He became private secretary to the Secretary of State for War, Antony Head, in 1956, and became Parliamentary Private Secretary (PPS) to Edward Heath in 1963, when Heath was Secretary of State for Industry, Trade and Regional Development and President of the Board of Trade. He was a member of the Executive of the 1922 Committee from 1964 to 1966, and resumed the position as Heath's PPS in 1967, when Heath was Leader of the Opposition. Kershaw represented the Conservatives at the Council of Europe and the Western European Union. After the Conservatives returned to power following the 1970 general election, Kershaw became a junior minister during the 1970–1974 Conservative government, first as Parliamentary Secretary in the Ministry of Public Building and Works (1970), then, after the death of Iain Macleod, as Parliamentary Under-Secretary of State at the Foreign and Commonwealth Office (1970–1973), and finally Parliamentary Under-Secretary at the Ministry of Defence with responsibility for the Royal Air Force (June 1973 – January 1974), replacing Lord Lambton who resigned after a sex scandal.