Nottingham Forest Mighten joined the
Nottingham Forest academy in 2009 after previously playing for
Arnold Town. During his development in the club's
Academy, Mighten received support from former Forest players
Des Walker and
David Johnson, as well as from Academy manager
Gary Brazil. On 24 September 2019, Mighten made his professional debut when he appeared as a 78th-minute
substitute during a 5–0 loss in an
EFL Cup fixture at
Arsenal. He signed his first professional contract three months later. He then made his first start for the Reds on 5 January 2020, in a 2–0 defeat to
Chelsea in an
FA Cup match; Mighten impressed in the game, winning a
penalty for Forest only for it to be ruled out by a marginal
VAR decision. He made his league debut on 22 February, in a 0–0 draw with
Queens Park Rangers at the
City Ground. He went on to make a total of eight
Championship appearances by the end of the
2019–20 season. He scored his first professional goal in a 1–1 draw at
Millwall on 19 December. He scored further goals against
Blackburn Rovers and Queens Park Rangers, ending the
2020–21 campaign with three goals in 27 appearances as he saw gametime under both
Sabri Lamouchi and
Chris Hughton. Supporters named him the club's Young Player of the Season. He again played 27 games in the
2021–22 season, this time scoring once against
Swansea City, and also featured once in the play-off semi-finals and was an unused substitute in the
play-off final win over
Huddersfield Town at
Wembley Stadium. On 29 August 2022, Mighten joined
League One club
Sheffield Wednesday on a season-long
loan. He made his debut a day later against
Bradford City in the
EFL Trophy, playing 80 minutes. His first goal at
Hillsborough came against
Morecambe in the FA Cup. He returned to Nottingham Forest on 10 January 2023 having played 14 times and scoring two goals, at times playing out of position at
wing-back and
centre-forward. Wednesday decided to end the loan as they were contributing a significant portion of the player's wages, much to Forest manager
Steve Cooper's frustration. As Mighten had already played for Forest and Wednesday in the
2022–23 season, this left him unable to join another club on loan and gametime for Forest in the
Premier League was an unreaslitic prospect. Wednesday manager
Darren Moore said that "it was one of the hardest decisions that I have had to make since becoming a manager". On 5 September 2023, Mighten moved on a season-long loan to
KV Kortrijk, who were bottom of the
Belgian Pro League. He featured 12 times in all competitions during a four-month stay at the
Guldensporen Stadion. However, eight of his league appearances were from the substitute bench. After being recalled by Forest on 9 January 2024, Mighten remained in Nottingham until transfer deadline day, when he was loaned to League One side
Port Vale for the remainder of the
2023–24 season.
David Flitcroft, the club's
director of football, said that "we look forward to watching Alex grow both on and off the pitch throughout his time with the club and with
Andy Crosby's team". However, Mighten missed four weeks due to a foot injury picked up in mid-March.
San Diego FC On 30 August 2024, Mighten signed with
Major League Soccer side
San Diego FC ahead of their inaugural season in 2025. Sporting director Tyler Heaps described his "unique and special qualities". The following day he joined
Danish Superliga club
Nordsjælland on loan for the remainder of the calendar year. ==International career==