A barber by trade, based in Glasgow, he became an active Trotskyist, joining the Revolutionary Socialist League.
Following a split in the Left Fraction in 1948, Selby became its leader, and he and his supporters increasingly came to dominate the Glasgow Govan Labour Party.
Eventually allowing the Left Fraction to peter out, Selby was able to win the Labour candidature in the 1973 Glasgow Govan by-election.
After his loss, it was reported by The Glasgow Herald that Selby's selection had been met with criticism from some Labour members who had felt that, at the age of 61, he was too old to be starting a parliamentary career.
[1] Selby stood again for the Labour Party in Glasgow Govan in the February 1974 general election, in which he took the seat by a narrow majority of 543 votes.