Bradford City, when he was sent off in the 66th minute after he pulled down Billy Clarke. He scored his first goals for Coventry when he scored twice in an EFL Trophy tie against West Ham Under-23s on 30 August 2016. He played five games in Coventry's run to the final, where Coventry defeated Oxford United 2–1 at Wembley Stadium to win their first trophy in 30 years. Turnbull played the final alongside Chris Stokes, a former teammate at Trowbridge Town, and said the day was "just a whirlwind and it was an unbelievable experience", and that winning the trophy alongside Stokes was a "special moment". After Coventry suffered relegation at the end of the season, Turnbull was expected to activate a clause in his contract which allowed him to leave, but on 31 July, the deadline to trigger the clause, he left on loan to Partick Thistle. Loan to Partick Thistle Turnbull joined Scottish Premiership club Partick Thistle on a one-year loan deal on 31 July 2017. After making 21 appearances in all competitions for The Jags, Turnbull was recalled from his loan in January 2018. Northampton Town The day after being recalled, Turnbull joined Northampton Town, for an undisclosed fee; the Coventry Telegraph reported there was no initial fee, but Turnbull had a sell-on clause should Northampton receive a fee for him as part of a future transfer. Signed by manager Jimmy Floyd Hasselbaink due to injuries to defenders Aaron Pierre and Leon Barnett, Turnbull had scored two goals against The Cobblers the previous season for Coventry. Despite being signed a cover for injuries, Hasselbaink said it wasn't a short-term signing, praising him for his experience and versatility. During his first full season at the club, Turnbull failed to start a game until October, but went on to make 34 appearances in all competitions following the sacking of manager Dean Austin, playing both as a defender and in centre-midfield. Continuing to play in midfield during the 2019–20 season, Turnbull began picking up regular bookings, and was suspended having received five yellow cards in eight games. Turnbull was reverted back to the defence with manager Keith Curle changing the formation of the team to a 3–4–3, and was a regular during the first half of the campaign. He missed three games between January and February 2020 after suffering a hip injury in an FA Cup match against Derby County.