Fanning was born in Dublin, but grew up in Roundwood
County Wicklow. He graduated from the Irish Racing Academy in 1986 and took a few rides for Irish trainer Kevin Connolly. In 1988, he moved to England to work for trainer Tommy 'Squeak' Fairhurst in
Middleham, Yorkshire, for whom he rode his first winner, over jumps, in a four-runner hurdle at
Sedgefield. He broke two neck vertebrae in a fall at
Newcastle after only three months and switched to flat racing. In 1990, he won his first flat race and within two seasons had lost his apprentice's claim. He now believes he was too light to have been a jump jockey in the first place. Without an apprentice claim, it was more difficult for him to win races, although he won the 1993
Northumberland Plate for trainer George Moore on Highflying. As a result, he began to ride out for another Middleham trainer, Mark Johnston. The pair first connected in 1990, although it wasn't until 1996 that the connection became strong. In 1998, he won his first Listed race, the Tote Silver Tankard at
Pontefract for Johnston. The following year, he won his first
Group race, the Group 3
September Stakes at
Epsom on Yavana's Pace, a horse on which he would also win the
Prix Gladiateur at
Longchamp two years later, almost to the day. He was also second twice in the
Irish St Leger on Yavana's Pace - in both 1999 and 2000. Darasim was his first Group 2 winner, taking the
Prix Kergolay in August 2003. The horse would later provide other big race victories in the 2003
Prix Gladiateur, the 2004
Betty Barclay Rennen in Germany, and the 2004
Goodwood Cup. In 2004, he secured more than £1 million in British prize money in a season for the first time. In 2006, he passed 100 winners for the first time. This was also the year of his first
Royal Ascot winner - I'm So Lucky in the 2006
Wolferton Handicap. Then, in 2007, he won the
King Edward VII Stakes at the Royal meeting on Boscobel, a horse on which he'd also won the Listed Glasgow Stakes at
Hamilton. Earlier in that same season, he won the
Lincoln on Very Wise for
William Haggas. However, also in 2007, he broke two vertebrae in his back when falling at
Goodwood and was out for seven months. Other Royal Ascot victories have come on Holberg (2009
Queen's Vase), Hartnell (2014
Queen's Vase) and two
Queen Alexandra Stakes on Oriental Fox in 2015 and 2017. His biggest single prize pot to date came in the
Goffs Million Mile at
The Curragh in September 2009 on Shakespearean, again for Johnston. He won more than 100 races in Britain every season from then until 2020, with his highest total to date of 188 coming in 2012. Also in that period, he twice won the All-Weather Jockeys' Championship - in 2009/10 and 2011/12. In 2014, he surpassed £2 million in British prize money for the first time. In September 2016, on his 46th birthday, he finally secured his first Group 1 victory on
The Last Lion in the
Middle Park at
Newmarket by three-quarters of a length at 25/1, having won the Group 2
Sirenia Stakes at
Kempton three weeks prior. Fanning later spoke of his satisfaction at winning a Group 1 after so many Group 2s and 3s "I wouldn't have liked to face retirement without that Group 1 so I did have a feeling of relief," he said. In 2023, he won the
Ayr Gold Cup for the first time on Significantly and rode The Gatekeeper, the 25/1 winner of the closing
Balmoral Handicap on British Champions Day at Ascot. For a short time in early-to-mid-season he headed the Jockeys Championship before eventually finishing 7th. He reached a mark of 2,500 winners in Great Britain on 24 August 2019 with a win at
Redcar on Universal Gleam for
Keith Dalgleish. He is one of only two active jockeys to reach that total and he has won more races since 1995 than any other jockey. As of the end of the 2023 flat season, he needed fewer than 200 to reach the 3,000 winner milestone, which he said was a little bit of a target for him. Besides the above injuries, he has also broken collarbones in falls at
Ayr and
Hamilton and his heel at
Wolverhampton in June 2017. In June 2022, in a fall from Braes Of Doune at
Musselburgh, he fractured his humerus and was sidelined for a large chunk of the busiest time of year, which contributed to his lowest seasonal total since the 1990s. He has ridden winners at every racecourse in Britain. He has described
Kieren Fallon at the height of his career as the most challenging jockey he competed against. ==Relationship with Johnston==