Queens Park Rangers Harriman made his professional debut on 23 August 2011 after being introduced as a 31st-minute
substitute for
Bradley Orr in a 2–0 defeat at home to
Rochdale in the
League Cup second round. On 10 November 2011, Harriman was
loaned to
Southern League Premier Division club
St Albans City for one month. He made his debut for St Albans two days later in a 4–1 win at home to
Evesham United, in which he assisted two goals from
Paul Furlong. Harriman finished the loan with 10 appearances. making his debut later that day as a 78th-minute substitute in a 1–0 defeat at home to
Exeter City. which he finished with 20 appearances. which would be extended until January 2014. The loan was extended until the end of the season on 7 January 2014, having made 24 appearances up to that point in
2013–14. Harriman scored his first professional goal in a 2–0 win at home to
Swindon Town on 18 January and completed the loan spell with one goal from 37 appearances. The loan was extended for a further month on 7 November, which would be extended for a third month on 8 December. Harriman scored his first goal for Luton in a 2–1 defeat away to
Cambridge United in the
FA Cup third round on 3 January 2015. His loan was extended until the end of
2014–15 on 16 January. Harriman scored Luton's second goal in a 2–0 victory at home to
Stevenage on 2 May, though they missed out on the play-offs to finish the season in eighth place. He completed the loan spell with 39 appearances and two goals. On 6 January 2016, Harriman signed for Wycombe permanently on a three-and-a-half-year contract for an undisclosed fee. Harriman was released when his contract expired at the end of the
2018–19 season.
Northampton Town Harriman signed for League Two club
Northampton Town on 4 September 2019 on a short-term contract until January 2020. He scored his first goal for Northampton in an
EFL Trophy second round tie against
Portsmouth on 3 December, in which they were beaten 2–1 away. Harriman was released by the club at the end of the
2021–22 season.
Non-League On 7 October 2022, Harriman signed for Southern League Premier Division Central club
Bedford Town. In March 2023, he joined league rivals
AFC Rushden & Diamonds. ==Managerial career==