[3] On 13 May 2014, he was in the Rangers side that won the Scottish Youth Cup beating Hearts 8–7 on penalties following a 2–2 draw, at St Mirren Park.
[7][8] After rejecting the offer of a new contract with Rangers, Telfer signed for Dundee United in June 2014, with a compensation payment still to be agreed between the clubs.
[11] He made his Dundee United debut as a substitute against Aberdeen in the opening match of the 2014–15 season,[12] and scored his first goal for the club in a 3–0 win over St Mirren on 1 November 2014.
Having been unable to gain a regular place in the Dundee United team, Telfer moved on loan to Scottish Championship side Livingston in January 2016 until the end of the 2015–16 season.
Morton manager Jonatan Johansson and his assistant Peter Houston walked out on the club before the final game of the season in May 2019, claiming that chairman Crawford Rae had told them not to select Telfer, as one further appearance would trigger an automatic contract extension.
[25] Telfer played a key role in helping Airdrieonians gain promotion back to the Scottish Championship via the play-offs at the end of season 2022-23.