Mullery was a tough but quick central midfield player who came through the ranks at Fulham as a youngster, making his debut in 1958. Within a year he was made captain after an injury to Johnny Haynes, though the special day turned into a nightmare when he scored an own goal.
After one game short of 200 for Fulham, Mullery joined Tottenham in March 1964 for £72,500 and settled quickly into the team. He was awarded his first England cap in Amsterdam as England drew 1–1 with the Netherlands in December of that year.
Mullery was an experimental choice by manager Alf Ramsey and didn't feature in subsequent England squads, nor was he selected for the final 22 who competed at the 1966 World Cup. But at Tottenham, his reputation as a strong midfield general and natural leader was beginning to emerge.
Tottenham won the FA Cup in 1967 after beating Chelsea 2–1, with Mullery's penetrating run from deep and blocked shot setting up the opening goal for Jimmy Robertson. In the same month, Mullery got his second England cap in an 2–0 victory against Spain at Wembley and stayed in the team ahead of his main rival, World Cup winner Nobby Stiles, as England progressed through the 1968 European Championship, reaching the last four.
Embarrassment and ignominy then struck Mullery, as he was given his marching orders for a retaliatory tackle on Yugoslavian player Dobrivoje Trivić, and became the first player ever to be sent off in a full England international match. England lost the semi-final 1–0. Stiles played in the third place play-off victory over USSR as Mullery served his suspension, but Ramsey kept faith with Mullery afterwards and had him back in the side for most of the friendly matches which would prepare England for their defence of the World Cup in Mexico.
Mullery, now Tottenham captain following the departure of Dave Mackay, won his 28th England cap when the tournament kicked off with a straightforward 1–0 win over Romania in Guadalajara. He stayed in the side for the remaining group games – a defeat against Brazil and a win over Czechoslovakia, which took England into the quarter finals, where they would meet the side they beat in the 1966 final, West Germany. Mullery was involved quickly, scoring his first England goal with a powerful near-post shot in the first half which put his side ahead, but England ultimately lost 3–2 (this despite going 2–0 up) and went out of the competition.
Ramsey continued to select Mullery after the tournament and named him England captain for their opening game in the qualification campaign for the 1972 European Championships, a 1-0 win in Malta. But with the likes of Colin Bell and Peter Storey coming through, Mullery played what turned out to be his 35th and final England game in October 1971, just a month short of his 30th birthday, in a 3–2 group game victory over Switzerland. Earlier in 1971, Mullery had lifted the League Cup as captain for Tottenham after a 2–0 win over Aston Villa at Wembley. A year later, he proudly held aloft the UEFA Cup after a 3–2 aggregate win over Wolverhampton Wanderers. Mullery scored the crucial Spurs goal in the second leg which separated the teams.
Mullery moved back to Fulham afterwards and scored what was later voted the BBC's Goal of the Season with an arching, swiping volley from 25 yards (23 m) during an FA Cup tie against Leicester City in January 1974. A year later, Fulham, a second division side, reached the 1975 FA Cup final with Mullery and his former England skipper Bobby Moore in the team, where they lost 2–0 to Moore's former club West Ham United. Mullery was subsequently appointed an MBE.
Mullery was the subject of This Is Your Life in 1976 when he was surprised by Eamonn Andrews at Craven Cottage.
In 1976, Mullery retired from playing and had a successful spell as manager of Brighton and Hove Albion between 1976 and 1981, taking them to two promotion campaigns and then keeping them in the First Division. He later managed Charlton Athletic (1981–1982), Crystal Palace (1982–1984) and QPR (1984), before later returning for a second spell at Brighton (1986–1987).
During Mullery's first spell at Brighton, he stoked the fire on an already-brewing rivalry between Albion and Crystal Palace. After some controversy involving a Brighton penalty being forced to be re-taken (the re-take was missed after the original kick was scored), Mullery publicly blasted the Crystal Palace management. When Mullery was later appointed Crystal Palace manager, in 1982, it prompted anger from Palace fans and a short-lived boycott from some Palace supporters.
Mullery replaced Terry Venables as manager of QPR in the summer of 1984. QPR had finished fifth in the First Division in the 1983–84 season under Venables before he left the club to join Barcelona. Mullery took over a QPR team that was involved in European football for the first time since the 1976–77 season.
Mullery guided QPR to a 7–0 aggregate win over KR Reykjavik in the 1st round of the 1984–85 UEFA Cup, but he was then involved in an extraordinary 2nd round UEFA Cup tie against FK Partizan. In the first leg, which was played at Highbury because of UEFA's ban on the artificial plastic pitch at Loftus Road, QPR beat Partizan 6–2, despite being 2–1 behind at one stage and down to ten men after QPR defender Warren Neill was sent off. In the second leg, Partizan won 4–0 in Belgrade to win the tie on away goals. Partizan's victory is, to date, one of only three occasions in the history of European competition where a team has overturned a four-goal first-leg deficit.
Mullery's QPR side were also involved in an extraordinary home league match in September 1984 against Newcastle United. At half-time Newcastle were 4–0 up after a hat-trick from Chris Waddle. But QPR came back after the break to draw the match 5–5. Mullery was sacked after six months in charge at Loftus Road just hours after QPR had beaten Stoke. In 1985, Mullery said that his time at QPR "turned me into a monster". He suggested that the players couldn't overcome their disappointment that Venables had left the club. Mullery blamed what he called "the moaning, groaning bunch of players who treated me, themselves and their profession with contempt" for killing his love of football.
After leaving QPR, Mullery stayed out of football management for 18 months until the summer of 1986, when he took over for a second spell as manager of Brighton. He lasted seven months before being sacked in January 1987. Mullery said of his sacking by Brighton: "You love the game, then it kicks you in the guts."
In the early 1990s, Mullery coached ATM FA in the Malaysian Premier League. He later served Barnet as Director of Football during 1996–1997.
Mullery had a brief stint as manager at Sussex non-league side Southwick F.C. He has worked for a number of years as a pundit for Sky Sports, and in September 2005 also briefly took a role with Conference club Crawley Town as a 'football consultant'.
In 2013, Mullery was appointed as Club Ambassador at his old team, Brighton and Hove Albion. His role includes matchday hospitality as well as working within the local community.
After leaving QPR, Mullery entered into a deep depression, worsened by an unsuccessful business venture; he converted to Christianity, though his financial and emotional troubles continued until he began working in the media in the mid 1990s.
Tottenham HotspurF.A. Cup winner – 1967
League Cup winner – 1971
UEFA Cup winner – 1972