Darling joined Cambridge United at the age of 12, but left a year later. After being spotted again playing for Newmarket Town's youth team, he rejoined the club in 2015. Darling joined the first team for pre-season ahead of the 2016–17 campaign. On 8 November 2016, he made his debut in a 2–0 EFL Trophy defeat to Scunthorpe United.[3]
He signed his first professional contract with the club in October 2016.[4] On 8 August 2017, Darling started in a 4–1 EFL Cup defeat at Bristol Rovers.[5] He made his full league debut for the club on 13 January 2018 in a 0–0 draw against Mansfield Town. On 17 August 2019, he scored his first professional goal, an 86th-minute winner against Colchester United.
Milton Keynes Dons
On 22 January 2021, Darling joined EFL League One club Milton Keynes Dons for an undisclosed fee,[6] and made his debut four days later in a 0–1 home defeat to Charlton Athletic.[7] Despite only being with the club since the January transfer window, he was named MK Dons' Young Player of the Year for the 2020–21 season having made just 21 appearances.[8]
On 31 August 2021, whilst captaining the side, Darling scored his first goal for the club, on his 100th start as a professional, in a 2–1 EFL Trophy group stage win away over Burton Albion.[9] He scored his first league goal on 27 November 2021, in a 4–0 away win over Morecambe.[10]
After an impressive first full season at the club in which he scored 10 goals in all competitions from centre-back, Darling was named in both the EFL League One Team of the Season and PFA Team of the Year[11] for 2021–22 alongside teammate Scott Twine.[12]