Born in Dublin, Devitt progressed through Hull City's youth system and was voted Young Player of the Year and Supporters' Club Player of the Year for the 2007–08 season. In 2009–10 he spent time on loan at three different League Two clubs. He signed for Darlington on a month's loan on 15 September 2009. He made his debut on 19 September in a 2–0 home defeat to Bournemouth, and scored his first goal for the Quakers in the last game of his loan spell, a 2–1 win against Shrewsbury Town on 17 October. On 22 October, only days after scoring against the club, he joined Shrewsbury Town on loan. He scored on his debut on 31 October 2009 against Notts County. His form dipped and he was deemed surplus to Shrewsburys promotion battle. He returned to Hull after being recalled in January 2010. On 17 February 2010 Devitt joined Grimsby Town on an emergency loan. He scored on his debut in a 1–1 draw against Notts County the same day. Against Grimsby's local rivals Lincoln City at Blundell Park the following Saturday, he picked up the Man of the Match award. Devitt's loan at Grimsby was extended until the end of the season on 24 March, after scoring three goals in seven appearances. The 2009–10 season was finished off for him with an unwanted hat-trick as he capped three relegations in one season. His parent club Hull City dropped out of the Premier League, while both Darlington and Grimsby were also relegated from League Two. He had a happier start to the 2010–11 season as he made his competitive first-team debut for Hull City by coming on as a substitute in their first match, a 2–0 victory over Swansea on 7 August 2010. Throughout the season, he made 16 appearance for the club. Devitt was on the substitutes bench but came on to set up a goal for Nick Barmby in a 3–2 loss against Wigan in the third round of a FA Cup. On 31 August 2011 Devitt signed with Bradford City on loan until January 2012. He made his debut for the club in the 1–1 draw at Morecambe on 3 September 2011. He scored in the 3–2 loss at Port Vale on 13 September 2011 and had set up a goal for Ritchie Jones. On 17 February 2012, joined League Two side Accrington Stanley on an initial one-month loan deal. Devitt made his debut in a 4–0 loss against Plymouth Argyle. One month later, Devitt scored his first goal in a 2–2 draw against Southend United, and the following week he scored another in a 2–1 win over Northampton Town. On 1 November 2012 Devitt signed an initial one-month loan deal from Rotherham United. However, after only making two appearances in all competitions, he had to return to his parent club due to an injury picked up in a 1–1 draw against Fleetwood Town. On 29 December 2012, amidst speculation Devitt would be re-joining Grimsby Town, Mariners boss Rob Scott distanced himself from the transfer by denying he has intentions to sign him despite previously being interested in the player. On 1 January 2013 Grimsby announced that they had made an enquiry about Devitt, but were waiting on the player and his agent to decide whether or not they were going to ask Hull for a pay-out if the situation was that he was not in the plans of the club. On 4 January 2013 Devitt re-joined Grimsby on loan for the rest of the 2012–13 season. In his second game back for Town he scored the equaliser in a 2–1 away win at Welling United that sent Grimsby into the quarter finals of the FA Trophy. In the quarter-final he opened the scoring with a free kick in Town's 3–0 victory over Luton Town. Town eventually made it through to the final at Wembley Stadium but were beaten by Wrexham on a penalty shootout after the game ended 1–1; Devitt was an unused substitute. In the league, Grimsby dropped off the pace and despite leading the Conference for majority of the season they eventually finished fourth and were defeated by Newport County in the play-offs. Devitt played 15 league matches for Grimsby, scoring two goals. On 16 May 2013, following Hull's promotion to the Premier League, Devitt was amongst a number of players released by the club. The following day amidst speculation of a return to Grimsby on a permanent deal Mariners joint boss Rob Scott said that Devitt had not done enough in his second spell to warrant a permanent move, and that Grimsby would not be pursuing any interest in Devitt.
Chesterfield
On 6 July 2013, Devitt played on trial for Chesterfield in the club's 3–0 pre-season victory over Buxton. After featuring two more successful pre-season trials for Chesterfield against Huddersfield Town and Nottingham Forest, he signed a six-month deal with the club. On 22 January 2014 Devitt moved on a month-long loan to Morecambe. He made his debut in a 2–2 draw at home to Portsmouth on 25 January 2014. In May 2014 Jamie Devitt was released by Chesterfield along with three other players.
Morecambe
On 19 May 2014 Devitt signed for Morecambe on a two-year deal after a successful loan spell at the Globe Arena.
Carlisle United
On 6 June 2016 Devitt signed for Carlisle United. He was offered a new contract by Carlisle at the end of the 2018–19 season.
Blackpool
On 20 June 2019, Devitt signed for Blackpool on a two-year contract, with the option of a further 12 months. In August 2019 he re-joined Bradford City on loan. His loan expired on 1 May 2020.
