Shortly afterwards, he was appointed manager of Queens Park Rangers. With a team containing the likes of Stan Bowles and Gerry Francis, as well as players recruited from ex-club Chelsea, John Hollins and David Webb, Sexton took Rangers to within a point of the League title in 1975–76. They were top after playing their final game, but Liverpool's late win over Wolverhampton Wanderers denied them.
He took over at Manchester United – again succeeding Tommy Docherty – but his reign was characterised by dour football and was not popular with the fans. In appointing Sexton it appeared as if the United board had again opted for safety following the tumultuous tenure of Docherty.
His reign at Old Trafford failed to deliver any trophies and in the pressure atmosphere that was engulfing United, Sexton seemed an inevitable casualty. The highlight was an FA Cup final appearance in 1979, losing 3–2 to Arsenal in a dramatic match, and finishing as league runners-up to Liverpool in 1979–80. Sexton was dismissed in April 1981, despite having won his final seven games in charge, and managed Coventry City before going into semi-retirement.
Sexton also had a very successful period as coach of the England's Under-21 side, and won the UEFA Under 21's Championship twice, in 1982 and 1984. After that he went on the become the FA's first Technical Director at the FA's National School at Lilleshall in 1984. He also wrote a book on coaching a soccer team for coaches of all levels called "Tackle Soccer."
| Team | Nat | From | To | Record | ||||
|---|---|---|---|---|---|---|---|---|
| G | W | L | D | Win % | ||||
| Leyton Orient | January 1965 | December 1965 | 37 | 7 | 20 | 10 | 18.9 | |
| Chelsea | October 1967 | October 1974 | 333 | 140 | 93 | 100 | 42.0 | |
| Queens Park Rangers | October 1974 | July 1977 | 130 | 57 | 41 | 32 | 43.8 | |
| Manchester United | July 1977 | April 1981 | 191 | 75 | 52 | 64 | 39.3 | |
| England Under-21s | 1977 | 1990 | ||||||
| Coventry City | May 1981 | May 1983 | 88 | 28 | 39 | 21 | 31.8 | |
| England Under-21s | 1994 | 1996 | ||||||