Swindon Town Gladwin began at
Reading's academy, and after being released played youth football with Eldon Celtic He began his senior career in
North Berks League Division One with
AFC Wallingford, winning their Player of the Season award in his first campaign aged just 17. He then spent time playing for various
non-League football teams such as
Salisbury City and
Hayes & Yeading United, before moving into professional football when
Swindon Town signed the midfielder from
Marlow in November 2013. Gladwin made his debut for Swindon on 10 December 2013, in a 1–1 draw at home to
Stevenage in the
EFL Trophy. His first goal for the club came the following season, in a 3–2 loss against
Plymouth Argyle in the same competition. On 14 April 2015, Gladwin scored a first-half hat-trick in a 4–2 win away to
Rochdale. On 11 May 2015, Gladwin scored twice in Swindon's 5–5 draw with
Sheffield United in the
Football League play-offs, but Swindon went on to lose in the final 4–0 against
Preston North End.
Queens Park Rangers On 28 May 2015, Gladwin and
Swindon Town teammate
Massimo Luongo, joined
Queens Park Rangers, both players signing on a three-year deal for an undisclosed fee. On 11 August 2015, Gladwin made his competitive QPR debut in a 3–0 win against
Yeovil Town in the first round of the
2015–16 Football League Cup. On 10 January 2017, Gladwin moved to
Swindon Town for a second loan spell until the end of the season.
Blackburn Rovers On 28 June 2017, Gladwin joined
League One side
Blackburn Rovers on a two-year deal. In November 2017, Gladwin suffered an injury for which he required surgery that ruled him out of play until February 2018. On 2 January 2020 he was released.
Milton Keynes Dons Gladwin signed for
Milton Keynes Dons on 10 January 2020 on a short-term deal. Despite several positive performances, he was initially one of nine players released by the club after the conclusion of the
2019–20 season. However, on 28 July 2020 the club announced Gladwin had returned and re-signed ahead of the
2020–21 campaign.
Swindon Town return Gladwin returned to Swindon Town on 26 July 2021 on a free transfer signing a one-year contract. After helping Crawley win promotion in the
2023-24 season, Gladwin retired from playing, citing his ongoing knee issues, and joined the club's coaching staff. ==Coaching career==