Duncan Idehen played for Norwich's Under-18s during the 2017/18 season, making his debut against Fulham on 25th November 2017. He is a midfielder.

On 1st July 2018 he moved to Lincoln City and a year later to Grimsby Town where he has broken into the first team making six appearances during 2020/21

Grimsby were relegated to the National League on 27th April 2021.

Idehen was released by Grimsby on 21st October 2021. After spending time with Birmingham's Under-23s, he signed for Bristol City on 1st January 2022. He made two appearances for the Robins in 2021/22.

On 18th August 2022 he was loaned to Carlisle and made five appearances, scoring once.

He spent 15 November 2023 to 31 January 2024 on loan to Yeovil making four appearances. On 22nd March 2024 he was loaned to National League South side Bath City.

Released by Bristol City, he signed for League of Ireland Premier Division side Derry City in August 2024. Manager Ruaidhrí Higgins, speaking on the club website, said of Idehen: "Duncan is a left-sided centre-back with fantastic athletic and physical attributes, with lots of opportunity for further development here in the League of Ireland."