[3] Born in Overtown, Lanarkshire, MacFadyen played junior football for Wishaw YMCA before beginning his Motherwell career in 1921.
[5] After leaving Motherwell, he played for Huddersfield Town, for whom he appeared in the 1938 FA Cup Final, and Clapton Orient.
[6] During the Second World War, he served in the Royal Air Force and was a guest player for Blackpool, Huddersfield, Nottingham Forest and Rochdale.
While he led the club to a memorable Scottish Cup giant killing against Celtic in 1949, he also oversaw United's record defeat when they lost 12–1 against the team where MacFadyen had been idolised as a player, Motherwell.
His son Ian was also a footballer who played for Dundee United's reserve side while his father was manager, then moved to Motherwell around the time Willie also left the club, returning to Tannadice for one season in 1959.