He signed a two-year professional contract with the club in October 2014. On 13 January 2015, McGeehan joined League Two club Cambridge United on a one-month youth loan. He made his debut four days later in a 4–0 win at home to Newport County, in which he scored twice and was named man of the match. Six days after his Football League debut, McGeehan made his first appearance in the FA Cup, playing in Cambridge's fourth round fixture with footballing giants Manchester United at the Abbey Stadium. He played for 90 minutes as Cambridge pulled off a shock result, holding the team 76 places above them in the football pyramid to a 0–0 draw. McGeehan's strong start to his Cambridge career continued, and he once again found himself on the scoresheet in a 1–1 draw with Dagenham & Redbridge. McGeehan received the first red card of his professional career in a 1–0 defeat at home to Wycombe Wanderers in what was to be the final match of his loan spell. On 14 February 2015, McGeehan rejoined Luton Town on loan until the end of 2014–15, with a view to a permanent transfer. He said that playing for Norwich's under-21 team was "pretty poor in terms of competitive football" and that he had "wanted to come back [to Luton] from the moment I left". McGeehan scored his first goal since returning to Luton in a 3–2 defeat at home to Morecambe. He scored a late winner on his 20th birthday in a 1–0 win away to Tranmere Rovers, to end a run of seven consecutive losses for Luton that had seen them drop out of the play-off places. On 1 July 2015, McGeehan joined Luton Town permanently on a two-year contract for an undisclosed six-figure fee, with a sell-on clause included. His first appearance after signing permanently came in a 3–1 win at home to newly promoted Championship club Bristol City in the League Cup first round on 11 August, before scoring Luton's second goal in the following match, a 2–2 draw with Oxford United four days later. McGeehan was introduced as a 60th-minute substitute in Luton's League Cup second round tie against Premier League team Stoke City, before scoring a last-minute equaliser to take the match to extra time. Luton eventually lost 8–7 on penalties, despite McGeehan netting in the penalty shoot-out.