He was shot outside of his home in north London. His killers Harry Duggan and Hugh Doherty, both of whom were members of what became known as the Balcombe Street Gang were captured and charged with his and nine other murders. They were sentenced to life imprisonment but freed in 1998 under the terms of the Good Friday Agreement. McWhirter was a sports journalist who helped co-found the Guinness Book of Records. In the early 1960s, he became a Conservative Party activist. In 1975, McWhirter co-founded the ultra right wing political organization National Association for Freedom. The organization initiated legal challenges against the trade union movement in the United Kingdom. He also advocated restrictions on the Irish community in Britain such as making it compulsory for all Irish people in Great Britain to register with the local police and to provide signed photographs of themselves when renting flats or booking into hotels and hostels. In doing so, McWhirter recognized that he could then be a target himself. In addition, McWhirter offered a £50,000 reward for information leading to a conviction for several recent high-profile bombings in England that were publicly claimed by the IRA. This was considered a 'bounty' by the IRA, a view that led directly to his assassination on November 27, 1975.