Gately joined Boyzone upon their formation in 1993. The group became known in Ireland after an infamous appearance on The Late Late Show that year, which presenter Gay Byrne dismissed—although he later concluded: “They certainly had the last laugh on us”. Boyzone’s first success outside Ireland was when the song “Love Me for a Reason” reached number two in the UK Singles Chart in 1995. The group split suddenly following a string of performances in Dublin’s Point Theatre in 2000. By the time Boyzone originally rested the band, they had achieved six number ones on the UK Singles Chart. They were considered a major pop band of the 1990s and had a much publicised rivalry with UK boy band Take That, even selling more singles than them. Gately shared the majority of lead vocal work with Ronan Keating.

Irish boy band Westlife said: “We are, like everyone else, in shock today. We met Stephen Gately back in 1998 when we first started out and since then had the pleasure of meeting him many times. Himself and the Boyzone lads paved the way for us as a band. Our thoughts are with Andy and the rest of his family, his friends, his legions of fans and of course his bandmates Keith, Mikey, Shane and Ronan who will be devastated at the loss of a truly beautiful person.” Former Taoiseach Bertie Ahern said: “It’s so sad. Boyzone and Stephen, they’ve all been part of Irish life and far wider than that, the last 15 years, and so successful, so it’s a huge, huge tragedy. He was 33 years of age, 15 years at the top, a fine musician, it’s just a huge tragedy to Irish entertainment, Irish music and further afield as well”. Minister for Arts, Sport and Tourism Martin Cullen paid tribute: “Stephen Gately was a gifted young man with a talent for singing which brought him tremendous success as a member of Boyzone and also as a West End star. There was a joy about his music making, and his death at such a young age is both a personal and professional loss”. Andrew Lloyd Webber said it is “a great loss to the musical world”. Elton John said he and his partner David Furnish were “stunned” when they heard the news. Katherine Jenkins twittered of “memories 2 cherish” from a night out in the weeks leading up to his death. Stephen Fry described Gately’s demise as “a dreadful shock”. “This was not supposed to happen. This was not in the script”, said music historian Paul Gambaccini.

Gately came out as gay in 1999 after discovering that an acquaintance was about to sell the details of his sexuality to the media.

After success with Boyzone, the band decided in 2000 to move on to solo projects. Gately was the first, with his debut solo single, “New Beginning”, released on 29 May 2000. The single reached number three in the UK charts.

The second single taken from the album was “I Believe”. Released on 2 October 2000, this song also featured on the soundtrack to the film Billy Elliot. The single just missed the UK top ten, peaking at number eleven. He attended the premieres of the film both at the Edinburgh Film Festival and at the Empire, Leicester Square, along with the stars of the film, Julie Walters and Jamie Bell. In May 2001, Gately’s third single, “Stay”, was released and reached number thirteen in the UK chart. That month, with his single still in the charts, his record company Polydor dropped him from their label.

From 2000 to 2002, Gately suffered from depression and addiction to prescription drugs.

In 2001 he made a cameo as himself in the fourth series of BBC sitcom Absolutely Fabulous, in that series’ opening episode ‘Parralox’.

In December 2002, Gately took the lead role in Bill Kenwright’s new production of Tim Rice and Andrew Lloyd Webber’s Joseph and the Amazing Technicolor Dreamcoat, which previewed in Oxford in December 2002 before moving to Liverpool over Christmas 2002 and finally to London’s West End and the New London Theatre in Drury Lane in February 2003. From September 2004 until March 2005 Gately played the Child Catcher in Chitty Chitty Bang Bang at the London Palladium.

Gately started dating Andrew Cowles, an internet businessman, who had been introduced to him by mutual friends Elton John and David Furnish. Gately and Cowles held a commitment ceremony in a wedding chapel while on holiday in Las Vegas in 2003. On 19 March 2006, Gately entered into a civil partnership with Cowles in a ceremony in London. The couple lived together in the north London village of Highgate. Gately spoke of his love for the village, saying he “wouldn’t move away for the world. It has a great vibe and the people here are brilliant”. In July 2009, their home was broken into by thieves who took £80,000 of items, including a prized Rolex watch which Gately had purchased with his first pay cheque. Gately was based in London for the rest of his life.

Gately made his pantomime debut at the Churchill Theatre in Bromley in December 2005 starring as Dandini in Cinderella. In April 2006 he took on the role of The Scarecrow in The Wizard of Oz at the Marlowe Theatre, Canterbury.

Gately also took part in Channel Five’s All Star Talent Show in October 2006, performing the slice and dice magic trick which he only had a week to learn, coming second to Toby Anstis. He was also in the second series of ITV’s Dancing on Ice with his dancing partner Kristina Lenko. They went out in eighth place on 10 February 2007.

In January 2007, Gately was heard in Horror of Glam Rock, a Doctor Who audio drama produced by Big Finish Productions for BBC7. For this audio play, Gately recorded an original song, “Children of Tomorrow”, with music by Tim Sutton and lyrics by Barnaby Edwards; this was his first solo track since 2001.

In September 2007, Gately began touring the UK in an 11-week run of Stephen Schwartz’s rock musical Godspell, but withdrew from the production after just three weeks for contractual reasons.

Gately grew up in relative poverty in the working-class Sheriff Street area of Dublin. He was the fourth of five children; his father Martin was a former decorator and his mother, Margaret (born 1949) a cleaner. His siblings are Michelle, Tony, Alan and Mark. He was particularly close to sister Michelle throughout his life. Gately’s father had an accident as a result of which he had to be hospitalised for three months from September 2004, and has not returned to work. His mother then took over as full-time carer. Gately attended primary school at St Laurence O’Toole’s and secondary school at North Strand Technical College. As a teenager he appeared in various musicals and theatre performances at school, such as Juno and the Paycock. He was estranged from his parents for years, but reconciled with them in 2008, and visited them with Andrew Cowles that year.

In 2008, Gately appeared in the independent horror film, Credo, which was released in the United States as Devil’s Curse.

In 2008 following his solo career and various bouts of acting and television appearances, Gately rejoined his old colleagues when Boyzone reformed, following the success of revived contemporaries Take That. Gately had been the most eager to reform and urged his bandmates to come together again. They sold out two more tours of the United Kingdom.

Boyzone released a brand new single, “Love You Anyway”, followed by a new compilation album in October 2008. December 2008 saw the release of a second new single, “Better”. The video for the song generated controversy, as scenes depicting romantic couples included a shot of two men embracing, in an inclusive nod to Gately’s homosexuality. The group unanimously agreed that Gately should be allowed to pair with a male actor. It was condemned by, among others, the minister of the Dromore Reformed Presbyterian Church. Others, however, cite that milestone as among the reasons why Gately is a “gay rights hero”. Wrote Tim Teeman of the Times Online, “Gately showed that an unflamboyant guy could be a pop star and gay…the real shame should be reserved for those managers and showbusiness power-brokers who practise that kind of discrimination, and also maintain the closet, to line their pockets.”

Gately was a vice patron of the charity Missing People (formerly National Missing Persons Helpline), supporting their Runaway Helpline service for young people. He was an ambassador for the Caudwell Children Charity in Stoke and on one occasion gave a private Christmas performance, raising thousands of pounds. Gately’s family requested that donations be given to the charity instead of flowers sent to them after his death in 2009. This in turn raised thousands more pounds. On one visit to a hospital he met a terminally ill child who admired the jacket he was wearing, and Gately allowed her to have it.

Gately died at his home in Port d’Andratx, Mallorca, early on 10 October 2009. His body was discovered later in the morning. His death was later determined to have been caused by a pulmonary oedema resulting from an undiagnosed heart condition.

Gately’s bandmates flew to Mallorca on 11 October 2009; The remaining members of Boyzone, Keith Duffy, Michael Graham, Ronan Keating, and Shane Lynch, issued a joint statement:

Fans responded with messages of sympathy on Twitter and Facebook. Thousands of pounds have been donated by fans to a Stoke-based children’s charity which Gately had endorsed. Searches for “Stephen Gately” was said to have “risen exponentially” and remained at the top for several days after the singer’s death and was later confirmed as being the most searched for topic on Google’s UK site in 2009. The search term “Boyzone” also ranked highly, being separated from “Stephen Gately” only by second-placed searches for “Nobel Peace Prize” following a controversial award to US President Barack Obama. Boyzone’s record catalogue was propelled back into the music charts. The single “No Matter What”, on which Gately is a prominent vocalist, received heavy play on radio.

Boyzone’s former manager Louis Walsh is quoted as saying: “We’re all absolutely devastated. I’m in complete shock. I was only with him on Monday at an awards ceremony. We don’t know much about what’s happened yet. I only heard after The X Factor (UK television talent show on which Walsh is a judge) and we will rally around each other this week. He was a great man.” Walsh dropped out of the live results show of The X Factor on 11 October 2009 as a direct result of Gately’s death. Simon Cowell addressed the issue at the start of the programme. He said: “This is really, really tragic news I want to send out my condolences to the family, our thoughts are with Louis”. That edition of the show attracted an “absolutely huge” audience which was said to have been seeking updates on the singer’s death. Walsh also was absent from the second week of The X Factor which coincided with Gately’s funeral,—later commenting: “I never want to watch the show at home again. I’ve been shouting at the TV all night”—at which Walsh was too upset to speak. My First Time, a stage show which was set to star bandmember Keith Duffy, was cancelled entirely. Duffy, Graham, Keating and Lynch had memorial “76 09” tattoos (Gately’s birth and death years) inked on their bodies when they brought Gately’s body home.

An article by Jan Moir in the Daily Mail on 16 October 2009 claimed: “Healthy and fit 33-year-old men do not just climb into their pyjamas and go to sleep on the sofa, never to wake up again. Whatever the cause of death is, it is not, by any yardstick, a natural one.” She suggested that drugs and a “dangerous lifestyle” were to blame for Gately’s death.

At the time of Gately’s death the group had selected thirty songs which they intended to record for a new album to be released in 2010. This was to have been followed by a tour.

The Tree of Seasons was written in collaboration with June Considine and Jules Williams. Based on Gately’s handwritten notes – the day he died he had just worked out the ending. The book released in the UK and Ireland on 13 May 2010, published by Hodder & Stoughton. It contains a foreword by Elton John and David Furnish, and is illustrated by Keith Wilson. The Tree of Seasons remained a best seller and a top ten seller for three consecutive weeks. The paperback version was released in April 2011.

Gately’s vocals will feature on Boyzone’s final album, in a song called “I Can Dream”. A video of the song was released on 15 June 2018, featuring images of Gately and Boyzone. The album is due to be released on the 16 November 2018.

In September 2020, Dublin City Council, agreed to name “Stephen Gately Park”, after the singer.