Tanner joined Reading's under-8s academy team in 2003.[4] In March 2011, Tanner signed his first professional contract with Reading, going through to the end of the 2014–15 season.[5] Tanner made his debut, and scored his first goal, for Reading in their 3–1 League Cup victory over Newport County on 12 August 2014, coming on as a substitute.[6]
On 22 January 2015, Tanner signed a new contract with Reading, lasting until the summer of 2017, and joined AFC Wimbledon on loan for the rest of the season.[7]
Plymouth Argyle (loans)
On 5 August 2015, Tanner signed for Plymouth Argyle on loan until 2 January 2016.[8] Tanner scored his first goal for the club, a stunning volley from the edge of the area, in a 2–1 defeat against Gillingham in the League Cup. On 6 January 2016, Tanner's loan at Plymouth Argyle was extended until the end of the season.[9]
On 18 August 2016, Tanner returned to Plymouth Argyle on loan until 16 January 2017,[10] extending his stay until the end of the season on 16 January 2017.
Motherwell
On 5 June 2017, Motherwell announced the signing of Tanner on a two-year contract.[11] He made his debut for the club away to Queen's Park in the group stage of the Scottish League Cup, scoring Motherwell's second goal in a 5–1 win.[12] He scored his first league goal on 30 September 2017, in a 3–0 win at home against Partick Thistle.[13] Tanner's first season at Motherwell ended early when he suffered a knee injury in training, described by manager Stephen Robinson as a "freak incident" which was expected to keep him out for up to six months.[14]
In November 2018, having twice undergone surgery on his injury, Motherwell assistant manager Keith Lasley announced that Tanner would remain out until at least January 2019.[15] Having failed to feature during the 2018–19 season, he was offered a short-term contract with a view to an extension upon his return to fitness.[16]
Having made his return to action he featured for Motherwell's reserve side. However, on 2 September 2019, he left the club having turned down their contract offer.[17]
Aldershot Town
On 9 December 2019, Aldershot Town announced the signing of Tanner on a contract until the end of the 2019–20 season.[18]