William John Mannion (born 5 May 1998) is an English professional footballer who plays as a goalkeeper for EFL League One club Charlton Athletic.

[4] He was a key member of the Under-18 team that knocked Premier League academies Watford and Newcastle United out of the FA Youth Cup before a fifth round defeat to Chelsea.

In May 2017, it was announced that Hull City would pay an initial fee of £100,000, plus further payments of up to £100,000 for appearances for the first team, and up to £225,000 should he become an Under-21 and full international in a competitive match.

[15] He joined National League North side Kidderminster Harriers on loan on 29 October 2019 until 25 April 2020 and played in 17 games for them.

[17] On 22 October 2021, Mannion joined National League South side Havant & Waterlooville on a one-month loan deal.