Starting his career with Motherwell, Johnny Porteous spent just over twelve months with Exeter City in the mid-1950s having joined the club from Plymouth Argyle where he had made in excess of 200 league appearances. He later played for Truro City.

After serving with the Royal Air Force during the Second World War, Johnny signed for Motherwell but didn't feature in the first-team during his two season stay. Subsequently playing for Alloa Athletic, he joined Plymouth Argyle in July 1949 for a reported fee of £2,000 and proved to be an immediate success at Home Park as he went on to make 215 league appearances with 13 goals along the way.

A member of Argyle’s promotion winning side of 1951/52, Johnny switched to Exeter City in March 1956 for £300 together with team mate George Willis. His first game for the Grecians came in the 3-1 home win over Northampton Town and, after making 13 league appearances in what remained of 1955/56, featured in 27 of the first 28 games in the following campaign until losing his place in January 1957. 

Asking for transfer in March 1957, Johnny left St James’ Park at the end of the season and signed for Truro City.

He died on 13 August 2007 in Plymouth.