Dundee Forsyth began his career with Carlogie Boys Club before joining
First Division side
Dundee in 2006. He was given his debut by manager
Alex Rae at the age of 17 in a 3–2 win at
Livingston on 11 November 2006. He joined
Third Division club
Montrose on loan in February 2008 until the end of the season. The
following season, Forsyth was loaned out to
Arbroath. He scored his first senior goal in a 1–0 win at
Brechin City on 28 March 2009. Having scored two goals in 26 league appearances for Arbroath, Forsyth returned to Dundee and established himself in the club's first team under the management of
Jocky Scott. Forsyth managed five more goals during the 2009–10 season, including the winner against
Inverness Caledonian Thistle in the
Challenge Cup Final. He helped Dundee finish sixth in the First Division the following season, despite the club being docked 25 points for entering administration. Forsyth made 33 league appearances and scored eight goals, including a brace in a 3–2 win against
Partick Thistle on 30 April 2011.
Watford In June 2011, Forsyth joined
Watford for an undisclosed compensation fee, and signed a three-year contract. He scored on his debut against
Burnley on the
first day of the season. in 2012
Bradford City (loan) On 19 October 2012, Forsyth joined
Bradford City on a two-month loan deal. He made his debut the following day, helping the team to a 3–1 win at home to
Cheltenham Town. He scored his first goal for the club on 4 December, completing a 2–0 win against
Port Vale in the
Football League Trophy.
Derby County (loan) On 4 March 2013, Forsyth joined
Derby County on loan, ahead of their match against
Cardiff City the following day, subject to clearance from
The Football League. Forsyth started against Cardiff City, before being replaced at 71 minutes in the 1–1 draw. Forsyth started as a makeshift left-back in his third game for Derby County against
Leicester City on 16 March 2013, assisting Derby's second goal which was scored by fellow loanee
Chris Martin in a 2–1 victory. Forsyth was recalled by Watford on 29 April 2013, a game before the end of the regular season. He played 10 times for Derby during his loan spell.
Derby County On 1 July 2013, Forsyth joined Derby County from Watford on a three-year contract for a reported fee of £150,000. Forsyth went into the
2013–14 season as first choice left back, with Clough stating Forsyth was also considered as an option at centre back in case of injuries and suspensions. Forsyth started the opening game a 1–1 draw at home to
Blackburn Rovers, his first game as a permanent player. On 27 June 2014, Forsyth extended his contract at
Derby County as he signed a new four-year contract to stay at the club until the end of the 2017–18 season. Forsyth suffered a cruciate knee ligament injury in November 2015, which kept him sidelined for nine months. On 22 August 2016, he suffered yet another serious injury, he did not return to action for another 12 months, after which he signed a contract extension in December 2017 until June 2020. On 10 November 2018, Forsyth suffered his third serious knee ligament injury during his Derby career, ruling him out of action for 379 days. He then had competition for the left back role in the form of academy graduates
Max Lowe and
Lee Buchanan during the
2019–20 season, he made 25 appearances during this season as his contract was extended until June 2022. In June 2020, Forsyth made his 200th appearance for Derby County. Lowe departed in August 2020, and Buchanan and Forsyth competed for the left-back role at the club, Forsyth played 21 times during the
2020–21 season. Then he played 29 times, scoring 3 times during the
2021–22 season in a season Derby were relegated to
League One after being deducted 21 points due to financial issues, Forsyth's second season playing for a club under
administration. Under new manager
Paul Warne Forsyth was regularly used as central defender. becoming the 30th player in Derby County history to do so. It was played against
Stoke City during the
2023–24 pre-season on 22 July 2023 at Pride Park. Derby won the game 3–0, which featured guest appearances from former teammates
Martyn Waghorn,
Craig Bryson,
Bradley Johnson and
David Nugent (Waghorn later signed again for the club). The game had an attendance of 9,119 fans. On 5 August 2023, Forsyth scored an equalising goal in Derby's first League One game of the season against
Wigan Athletic, although Derby went on to lose the game 2–1. Forsyth scored in wins over
Barnsley on 11 November 2023 and
Oxford United on 29 December 2023. He started in 24 of Derby's first 25 League One matches of the season, but that run of starts was ended when he sustained a
calf muscle injury at
Fleetwood Town on 6 January 2024. Paul Warne said that Forsyth would be out of the "foreseeable" with the injury. Forsyth returned to action on 12 March 2024, after two months on the sidelines, but suffered another calf injury later on in March. He was unable to make a return to action that season, when Derby won automatic promotion to the Championship. Forsyth made 32 appearances for Derby with three goals during 2023–24. On 18 May 2024, it was announced that Forsyth had trigged a one-year performance-based clause to extend his contract at Derby until June 2025,
the 2024–25 season will be his 13th at the club. On 28 September 2024, Forsyth made his 300th league appearance for Derby, in a 3–2 loss to
Norwich City, Forsyth had involvements in both Derby goals in the match with a goal and an assist. Forsyth would find himself managed by former teammate
John Eustace later in the 2024–25 season, scoring in Eustace's first win as head coach. After injury to
Callum Elder, Forsyth played at left-wing back under Eustace and with key goals and assists, he helped Derby retain their Championship status. Forsyth played 42 times for Derby during the season, scoring three times. In May 2025, Derby County confirmed that Forsyth was in talks with Derby to extend his contract which expired in June 2025. On 23 June 2025, it was announced the Forsyth had signed a two-year extension to his Derby County contract until the end of the 2026–27 season, which would upon expiry of his new deal ensured he spent 15 seasons at Pride Park. He would also be working towards his
UEFA coaching licences to transition into a possible coaching role after his playing career had concluded. On 24 February 2026, Forsyth scored on his 37th birthday; in a 4–2 loss to
Hull City. On 11 April 2026, Forsyth made his 400th appearance for Derby County in a match at
Southampton, becoming the 15th player in club history to do so. ==International career==