William George Longmuir (born 10 June 1953) is a Scottish professional golfer.

Longmuir may be best known to international audiences for his performance in the 1979 Open Championship at Royal Lytham & St Annes Golf Club.

He shot a second round 74 but, in the difficult conditions, was still in solo third place only one behind Seve Ballesteros and three behind Irwin.

The award goes to the British golfer who shot the lowest single round in the Open Championship.

At the 1984 Open Championship at St Andrews he shot 67 (-5) to hold the lead with Peter Jacobsen and Greg Norman.

In his rookie season he won two events and finished runner-up on the Order of Merit.

[1] In 2006 he played on the United States-based Champions Tour after coming through its Qualifying School.

European Tour playoff record (0–2) Note: Longmuir only played in The Open Championship.