[1] He studied at Campbell College in Belfast and joined the Ulster Unionist Party (UUP) in 1938.
He was commissioned into the 8th Anti-Aircraft Regiment, Royal Artillery in 1939 and served during World War II, reaching the rank of Captain.
[2] In 1969 Hall-Thompson standing as an unofficial Unionist supporting the more moderate policies of the Prime Minister of Northern Ireland Terence O'Neill, unseated the incumbent Unionist MP for his father's old seat of Belfast Clifton in the Parliament of Northern Ireland.
[1] Following the abolition of the Parliament, Hall-Thompson was elected to the 1973 Northern Ireland Assembly for Belfast North, representing the UUP.
The following year, he became the leader of the Assembly and also the Executive's Chief Whip, before joining the Unionist Party of Northern Ireland.