McGuigan began his juvenile boxing career at the Wattlebridge Amateur Boxing Club, County Fermanagh and later moved to the Smithborough Amateur Boxing Club, County Monaghan. Under the guidance of trainers Danny McEntee and Frank Mulligan he rapidly established himself as an exceptional boxer. He won the All Ireland Amateur Championship in 1976 having defeated Martin Brereton. Notable opponents during his teenage years included Dubliner James Coughlan, whom he defeated at the age of 15, as well as Gordon McNeil (of Heaton, Newcastle upon Tyne) and Eric Clarke (of Hackney, London).

As an amateur, McGuigan represented Northern Ireland in the Commonwealth Games at Edmonton in 1978 and represented Ireland at the 1980 Summer Olympics in Moscow. He became a British citizen so that he could compete for British titles.

He began his professional boxing career on 10 May 1981, beating Selvin Bell by TKO in two rounds in Dublin. After another win, he suffered his first setback, losing a hotly disputed decision to Peter Eubank (brother of Chris Eubank) over eight rounds at Corn Exchange at the Brighton Dome. After his first loss, McGuigan notched up two more wins, including one over Terry Pizzarro, and then he was given a rematch with Eubank. The second time around, McGuigan prevailed, by a knockout in the eighth round.

In 1982, McGuigan won eight fights, seven by knockout. One of these, however, almost destroyed his career and his life. Opposed by Young Ali, on 14 June 1982, McGuigan won by a knockout in six rounds; Ali fell into a coma from which he never recovered. According to the book The Ring: Boxing The 20th Century, this affected McGuigan so much he was not sure he wanted to carry on as a boxer. He also defeated Paul Huggins and Angelo Licata during this period. In 1983, he won four fights, winning the British Title against Vernon Penprase, and including his first trip to fight outside Europe (when he beat Samuel Meck by a knockout in six in Ontario, Canada), before getting his first try at a European title.

On 16 November, Italy’s Valerio Nati boxed McGuigan for the vacant European Featherweight title in Belfast, and McGuigan won the crown with a knockout in the sixth round. He then became the number one Featherweight challenger in the World Boxing Association. In 1984, he won six bouts, all by knockout. Among the fighters he beat were former world title challengers Jose Caba and Felipe Orozco. He also beat contenders Paul DeVorce and Charm Chiteule and retained his British and European titles against Clyde Ruan and the latter belt against Esteban Eguia to keep his chance at a World Championship attempt alive.

He was honoured in an Irish ballad song released in 1984, “Clones Cyclone”, written by Johnny McCauley and sung by Big Tom. The popular German musician and composer Udo Lindenberg also dedicated his song “Jonny Boxer” to McGuigan in 1986. The Bournemouth-based band The Worry Dolls named a track “Barry McGuigan” on their album, The Man That Time Forgot.

In 1985, McGuigan met former world featherweight champion Juan Laporte and won by a decision after ten rounds. Following one more win (a defence of his European Title against Farid Gallouze), he finally got his world title try when the long reigning WBA featherweight champion, Eusebio Pedroza of Panama, went to London to put his title on the line at Loftus Road football stadium. McGuigan became the champion by dropping Pedroza in round seven and winning a unanimous fifteen-round decision in a fight refereed by hall of fame referee Stanley Christodoulou. McGuigan and his wife were feted in a public reception through the streets of Belfast that attracted several hundred thousand spectators. Later that year, he was named BBC Sports Personality of the Year, becoming the first person not born in the United Kingdom to win the award.

McGuigan made his first defence against American Bernard Taylor, who was stopped in the ninth round, and then against Danilo Cabrera, who got knocked out in fourteen rounds. This proved to be a controversial stoppage: the fight was stopped after the challenger bent over to pick up his mouthpiece after losing it, a practice that is allowed in many countries but not in Ireland. Cabrera was not aware of this, and the fight was stopped. Although Cabrera’s corner protested the outcome, McGuigan remained the winner by a knockout. For his next defence, he went to Las Vegas in June 1986, where he faced the relatively unknown Stevie Cruz from Texas in what proved a gruelling fifteen-round title bout under a blazing sun. McGuigan held a lead halfway through, but suffered dehydration because of the extreme heat and wilted near the end, being dropped in rounds ten and fifteen. He eventually lost a close decision and his world belt, which he was never to reclaim. After the fight, McGuigan required hospitalisation because of his dehydrated state.

After that fight he retired, partly due to the death of his father in 1987. He used to say his father was his greatest inspiration and, after his death, apparently felt no reason to continue boxing. However, he returned to the ring between 1988 and 1989, beating former world title challengers Nicky Perez and Francisco Tomas da Cruz, as well as contender Julio César Miranda, before losing to former EBU featherweight champ and future WBC and WBA super featherweight challenger Jim McDonnell by a technical knockout when a McDonnell left hook opened a gash over McGuigan’s right eye in 2nd round that caused the referee to stop the fight in the 4th. He retired permanently from boxing. His record was 32 wins and 3 losses, with 28 wins by knockout. In January 2005, McGuigan was elected into the International Boxing Hall of Fame.

McGuigan lives near Whitstable, Kent with his wife and children. He currently works as a boxing pundit for Sky TV. He has tried his hand at acting, appearing in the movie Malicious Intent in 2000. He also served as referee on the UK television game show Grudge Match, hosted by Nick Weir.

McGuigan was inducted into the World Boxing Hall of Fame and International Boxing Hall of Fame in 2005. He also fought in Ring Magazine’s 1986 Fight of the Year, and was a title character in the 8-bit computer game, Barry McGuigan World Championship Boxing. In 1985 he was voted BBC Sports Personality of the Year.

Two biographies of McGuigan have been written. He appeared in the third series of ITV’s Hell’s Kitchen in September 2007, where he was eventually crowned the winner after winning the public vote.

In August 2009, he co-presented Charity Lords of the Ring with Lucy Kennedy.