Duncan was born an entertainer, starring in school productions and starting his professional career working at a Haven holiday camp, where he was to meet his soon-to-be bandmates Lee Ryan, Simon Webbe and Antony Costa. Blue, the pop group, was born in 2001 and the band immediately signed to Innocent Records.
They exploded onto the scene and amassed huge commercial success, racking up 40 Number One singles worldwide, three Number One UK albums and sales of over 16 million records.
In 2005 the guys decided to take a break from the band to pursue other interests, and Duncan saw this as the perfect opportunity to broaden his experience within the entertainment industry. He starred as Billy Flynn in the hit musical Chicago, and became a familiar face on television, working as a presenter on Soapstar Superstar, Capital FM's Party In The Park, City Hospital, T4, The Clothes Show and GMTV’s Entertainment Today. He also competed in ITV's Dancing On Ice in 2007 where he became a finalist, and participated in the subsequent sell-out tour in arenas across the UK. He then made his television acting debut in Plus One for Channel 4, in which he played a tongue-in-cheek characterization of his Blue persona, with the series being acclaimed by both critics and the public. Further TV appearances have included Grease: The School Musical for Sky 1, Eurovision: Your Country Needs You (as a Judge) for BBC1, Eight Out Of Ten Cats for Channel 4 and presenting The National Lottery for BBC1 many times.
In 2009 Duncan returned to theatre, appearing as Warner Huntington III in the West End production of Legally Blonde at the Savoy Theatre. He then presented the exciting new theme park game show Scream If You Know The Answer on Watch in 2010, which played a second series in 2011, before landing a spot on the judging panel on Channel 5's new entertainment show Don't Stop Believing, searching for the group that best represented the spirit of the Glee phenomenon.
2011 saw the Blue boys come 11th representing the UK at the 2011 Eurovision Song Contest in Düsseldorf with "I Can". The band released their fourth studio album, Roulette, in 2013 with "Hurt Lovers" as the lead single, before they joined other groups on TV in The Big Reunion. Blue continued to thrive with a new album in 2015, and a new TV show on ITV2 – Blue Goes Mad In Ibiza, which followed the band as they launched their own bar.
Duncan went on to play the role of Ryan in the popular Channel 4 soap opera Hollyoaks. For his role as Ryan, Duncan was nominated for Most Popular Newcomer for the 2016 NTA's and was nominated for Best Newcomer for the 2017 Soap Awards.
2015 also saw Duncan return to the stage, starring as Tick in the UK tour of Priscilla Queen of the Desert. He made his pantomime debut in 2014/15 playing the title role in Jack and the Beanstalk at the Birmingham Hippodrome for Qdos Productions. Duncan starred as Prince Charming in Cinderella at the Liverpool Empire in 2017/2018. In 2018 he reprised his role of Billy Flynn in the West End's production of Chicago. In 2019, he starred as Frank-N-Furter in the UK and Ireland tour of The Rocky Horror Show.