The Blue singer will play Ryan, the head of a new family who have just moved into the village, in the Channel 4 series.
Duncan confirmed the news on Twitter, writing: “Thrilled 2 finally announce & confirm I am about 2 start a new chapter in my life as a full time member of the @Hollyoaks cast. Can't wait."
The 38-year-old star is best known for being one quarter of the British boyband Blue, who formed in 2000 and went on to score many hits including ‘All Rise’ and ‘One Love’, and three UK number one albums.
The band, which also includes Lee Ryan, Simon Webbe and Antony Costa, represented the UK at the 2011 Eurovision Song Contest, finishing in 11th place.
Speaking about his new role, Duncan said: "I’m looking forward to working with the fantastic on and off screen talent on the show and bringing the character of Ryan to life.”
A spokesperson for the show added: "Ryan is a good guy in a committed relationship who will move into the village. He is a grounded family man with principles and integrity but who will fight tooth and nail for what he believes in."
It’s not the first time Duncan has acted, having performed in West End musicals, including ‘Chicago’ as Billy Flynn and alongside Sheridan Smith in 'Legally Blonde: The Musical'.
He is currently touring the UK in a stage production of ‘Priscilla: Queen of the Desert’.