Keating was born on 3 March 1977, the youngest of five children. He grew up in Bayside in Kilbarrack, County Dublin, and in County Meath, attending St. Fintan's High School. His father, Gerry Keating, was a lorry driver; his mother Marie was a mobile hairdresser. He has one sister: Linda, and three brothers: Ciarán, Gerard and Gary. He competed in track and field, winning the All Ireland under-13 200 m title.

In 1993, the then 16-year-old Ronan Keating was the youngest member to join Boyzone. Keating, Keith Duffy, Richard Rock, Shane Lynch, Mark Walton and Stephen Gately were chosen as Boyzone members. Walton and Rock would later leave the group before being replaced by Michael Graham. The group performed in various clubs and pubs before being signed by PolyGram in 1994 and released a cover version of "Working My Way Back to You" by The Four Seasons. The group also released a cover version of "Love Me for a Reason" which would peak on several charts. In 1998, his mother died at the age of 51 from breast cancer, resulting in the establishment of the Marie Keating Foundation.

At the age of 21 years, Keating married Yvonne Connolly in April 1998 and together, the couple have three children: Jack (born 15 March 1998), Marie (born 18 February 2001) and Ali (born 7 September 2005). The couple are now divorced after Keating had an affair. From 1994 to 1999, Boyzone released 17 singles, 3 studio albums and 1 compilation album before disbanding in 2000 selling 27 million records and 3 million records from 4 singles, 1 compilation and studio album since their reformation.

In 1999, while still a member of Boyzone, Keating recorded a version of "When You Say Nothing at All" for the motion picture Notting Hill. The single peaked at number one in the UK charts, leading to a successful solo career. Keating released his debut solo album, titled Ronan, in 2000, which peaked at number one in the UK Albums Chart. The album was given several negative reviews, although it sold over 750,000 copies and became one of the top selling albums of the year in the United Kingdom. It debuted at number one on the UK Albums Chart, and has been certified four-times platinum by the British Phonographic Industry for sales of 1.2 million copies. In the singer's native Ireland, the album debuted at number two. The album also became a commercial success in other European countries, where it charted within the top ten of eight countries. In 2001, Ronan was certified two-times platinum by the International Federation of the Phonographic Industry for shipments of two million copies inside Europe.

The album produced four UK and Irish top-ten singles: "When You Say Nothing at All" (originally recorded for the soundtrack of the 1999 film Notting Hill), "Life Is a Rollercoaster", "The Way You Make Me Feel", and "Lovin' Each Day", the latter of which was featured on the re-release edition of the album, and later on Keating's second album, Destination (2002). Also the song "Lovin each day" is from a movie "Summer catch".

On 5 November 2007, Keating confirmed that Boyzone would reunite for a special appearance on the BBC's annual fundraiser, Children in Need, performing a medley of hits, although had not yet commented on the possibility of a new tour or album. Soon, they went on a 29-date tour, taking in cities such as Cardiff, Newcastle, Liverpool, London at the O2 Arena and Wembley, Manchester, Birmingham, Glasgow, Aberdeen, Sheffield, Newcastle, Nottingham, Edinburgh Castle and the RDS in Dublin. A greatest hits collection was released and two new singles in 2008 selling 700,000 copies.

Stephen Gately, a close friend and bandmate of Keating, died on 10 October 2009 of a pulmonary edema. In 2009, Keating co-wrote the song "Believe Again" sung by Niels Brinck, who won the Dansk Melodi Grand Prix and represented Denmark in the Eurovision Song Contest 2009 in Moscow where it qualified for the final from the second semi-final and finished in 13th place with 74 points. Following the success of the album Songs for My Mother, he has recorded another entitled Winter Songs. Teaming up again with Songs for My Mother producer Steve Lipson, Keating pulled together eleven songs that evoked memories of winter and Christmas for him. Winter Songs is a mix of traditional and modern festive classics, including tracks from artists such as Simon & Garfunkel, Joni Mitchell and Sugarland along with perennials "Silent Night" and "Have Yourself a Merry Little Christmas". The album also includes two and new songs, "It's Only Christmas" and "Scars".