Gillard started out at Tottenham Hotspur in the youth ranks before moving to West london and QPR where he made his debut in November 1968. Over the next fourteen years he made the left-back position virtually his own forming a formidable full-back partnership with Dave Clement for many seasons. He was an integral member of the 1975-76 team that almost won the First Division title, eventually finishing as runners-up to Liverpool.
His last game for QPR was in the FA Cup final replay against Tottenham Hotspur in 1982. He then moved on a free transfer to Aldershot taking up a position as player coach. He played 408 league games (485 in all competitions, which is the third highest in the club's history) and scored a total of 11 goals. Ian won 3 international caps for England in 1975.