At 20 Templeton wrote the one-act play The King's Spaniel, which ran at the Royal Lyceum Theatre, Edinburgh.

In 1937, his first three-act play Circus Murder, was picked up and produced by Jevan Brandon Thomas at the Theatre Royal, Glasgow, then exported to London by the producer Esme Church for a run at the West End's Noël Coward Theatre (1938) under the title The Painted Smile.

"[2] After being decommissioned from the RAF after World War II, Templeton wrote several West End plays in succession[3] including: Sunday Times theatre critic James Agate wrote that Exercise Bowler "has an immense amount to say, is inventive, brilliantly theatrical and magnificently laid out for actors."

In 1950, Templeton's screenplay adaptation of the book All On A Summer’s Day by HLV Fletcher became the British crime thriller Double Confession directed by Ken Annakin, starring Peter Lorre.

[6] In television, Templeton contributed to several prime time series of the period, including: The Alcoa Hour (1954–57);[7] The Untouchables (1960); the original Adventures of Robin Hood[8] (1957) with Richard Greene; and the Westinghouse Desilu Playhouse[9] anthology series broadcast by CBS from 1948 to 1958 and produced by Desi Arnez.