The footballer John Dempsey, who has died aged 78, was an uncompromising central defender with Chelsea when they won the FA Cup in 1970 and the European Cup Winners’ Cup in 1971. Although most accustomed to clearing out attackers and winning balls with his aerial power, Dempsey made significant attacking interventions in both those triumphs, in particular during the European Cup Winners’ Cup final replay in Athens against Real Madrid, when on a rare excursion into the opposition penalty box he came up with a crisply struck volley from 12 yards to set Chelsea on the way to a 2-1 victory. He also contributed a headed goal in a fifth round defeat of Crystal Palace during the victorious FA Cup campaign of the previous year.

Those goals – two of only seven he scored in his 207 matches for Chelsea between 1969 and 1978 – gave a clue to Dempsey’s schoolboy exploits as a striker. But his primary concern was to shore up the defence, in combination with the rugged trio of David Webb, Ron “Chopper” Harris and Eddie McCreadie, described by their teammate Peter Osgood as the “four assassins at the back”.

Though he was an unassuming character in a team with plenty of big personalities, Dempsey was a popular, fun presence in the dressing room and a well-regarded figure on the terraces. Long-haired but prematurely balding, he nurtured a comb-over that was audacious even by the standards of the time.

As Chelsea struggled to maintain their momentum from 1972 onwards, injury began to dog his progress, and after leaving the club to play in the US he retired from all football in 1984, having also made 19 appearances for Ireland between 1966 and 1972.

Dempsey was born to Irish parents, Molly and Thomas, in Hampstead, north London, and grew up in nearby Kilburn, where from the age of six he was taken by his father to watch Chelsea one week and Fulham the next. Fulham spotted him playing Sunday league football as a centre-forward for the Iverson club in Regent’s Park, and secured his services as a 15-year-old apprentice, straight from Kynaston school (now Harris academy) in St John’s Wood.

Making his debut for the First Division club in 1964, at 6ft 1in and already with impressive heading ability, he spent some of his early games as an attacker, scoring a 19-minute hat-trick in the League Cup against fellow top-flight team Northampton in 1965 before switching solely to central defence.

The Chelsea manager Dave Sexton took Dempsey to the more glamorous setting of Stamford Bridge for a £70,000 fee in 1969, and immediately his horizons widened. The FA Cup final win arrived in his first full season with the club, in a memorable and fiercely contested pair of matches against Leeds at Wembley and Old Trafford.

His goal in the European Cup Winners’ Cup final the following year came when the opposition keeper punched out a Charlie Cooke corner and he pounced on the ball, hitting it sweetly before it could touch the ground. “Nine times out of 10 it would have gone anywhere, but thank God it went into the roof of the net,” he said. “It was a fantastic feeling, and the groundsman told me it was the best goal he had ever seen on that pitch.”

There was another cup final appearance in 1972 as Chelsea lost at Wembley to Stoke City in the League Cup, but later on Dempsey missed a whole year due to achilles tendon and toe injuries, and by the time Chelsea had fallen down to the Second Division in 1975 he was unable to reclaim a regular place in the team.

His largely uneventful playing career for Ireland, for whom he was qualified through his parentage, ended in 1972, two years after he had become the first Irish international to be sent off – for throwing the ball in annoyance at the referee during a game against Hungary.

At the age of 32 Dempsey left Chelsea for two years in the US with Philadelphia Fury, where he was reunited with Osgood and was voted the North American Soccer League’s defender of the year in his first season, beating Franz Beckenbauer into second place.

Spending 1981 and 1982 as player-manager at non-league Maidenhead United, he had brief spells in the same position with the League of Ireland side Dundalk in 1983 and then with Egham in Surrey before retiring the following year.

Afterwards he moved into a lengthy career working with people with learning difficulties in Edgware, north London, first at the Springwood Crescent Centre, as a physical education and sports instructor, and then at Broadfields Resource Centre, in charge of its sports programmes. That work, he maintained, was every bit as enjoyable and rewarding as his exploits on the football field.

Dempsey is survived by his second wife, Trish, and two children, Louise and Paul, from his first marriage to Margaret, which ended in divorce.

• John Thomas Dempsey, footballer, born 15 March 1946; died 6 November 2024