After being out of favour, he asked for a transfer and joined Leeds United for £33,000. “I am going to haunt him”, is what Giles said of Busby, to his wife Anne, after the Scotsman had forced his departure when freezing him out of the starting team.
Giles would soon evolve into one of the finest central midfielders in England, as Leeds won the Second Division title in his first season there. In 1965, he was in the team which came close to a League championship and FA Cup “double” but missed out on both, to Manchester United and to Liverpool respectively.
Giles formed a strong partnership with Billy Bremner as Leeds manager Don Revie built a new team around them. The players had similarities in their styles and were a tremendous foil for one another. Giles was known as the creative force and Bremner as the ball-winner, but each was capable of doing the other’s primary job.
In the 1967–68 season Leeds won both the League Cup and the Fairs Cup. That was the first season in which Giles was affected by injury, which meant he missed the second leg of the Fairs Cup final. In the 1968–69 season, Giles was instrumental in Leeds becoming league champions in a then record 67 points from 42 matches at 2 points for a win, a record that stood for ten seasons. In 1970, Giles again had a magnificent season as Leeds chased three trophies but lost all three, the League went to Everton; the FA Cup to Chelsea after a replay; and the European Cup campaign ended at the hands of Celtic in the semi-finals.
In the fifth round of the 1971 FA Cup, when Leeds were unexpectedly beaten 3–2 by Colchester United, Giles scored Leeds’ second goal as they almost came back from 3–0 down. Leeds regained the Fairs Cup but lost the League title on the last day, with Arsenal getting the victory they needed to earn the championship and form one half of a successful “double” bid.
Leeds won their first FA Cup and Giles his second when they defeated Arsenal 1–0 at Wembley in 1972, yet again they missed out on the League on the final day of the season after defeat to Wolverhampton Wanderers. Sunderland and A.C. Milan beat Leeds in the finals of the FA Cup and the European Cup Winners Cup in 1973, rendering Leeds trophyless again. Jack Charlton’s retirement in 1973 also left Giles as the most senior member of the squad. In the same year he started to combine his Leeds duties with a spell as player-manager of his country.
In 1974, a 29-match unbeaten run at the start of the season helped Leeds coast to their second title, but then controversy reigned after Revie quit to take over the England team. Revie recommended to the Leeds board of directors that Giles, nearly 34 and approaching the end of his playing career, should be his successor. The board instead appointed Brian Clough, a brilliant manager but a controversial choice as he had been publicly critical of Leeds in the past and was not an admirer of Revie. Clough and the players never got on – the players had wanted Giles too – and the board reacted by dismissing Clough with a big pay-off after just 44 days in charge. Giles still did not get the job though (that went to Jimmy Armfield) and concentrated on playing as Leeds chased a place in their first European Cup final. Giles himself never applied for the Leeds vacancy on those two occasions, his name had instead been put forward as a candidate by others. Also in 1974, Giles was nominated—along with Danny Blanchflower—by Bill Nicholson as his successor at Tottenham Hotspur. The Spurs board appointed Terry Neill instead.
Giles was outstanding in Leeds’ European campaign but was no longer an automatic fixture in the side. After appearing in the 1975 final, which Leeds lost 2–0 to Bayern Munich, Giles accepted an offer in June 1975 from West Bromwich Albion to become their player-manager, while still playing for and managing the Irish team.