His debut season earned him a move to Welsh Premier League side Airbus UK Broughton in Summer 2010, and his impressive appearances for the club in a series of pre-season games saw him immediately depart for Wolverhampton Wanderers. He signed a two-year deal (with an option for a third) with the English Premier League side for an undisclosed fee following a short trial.

Cassidy was capped by Wales at both under-19 and under-21 level. He scored once for the under-19s, against Scotland in September 2011.

In March 2012, he moved on loan to League One side Tranmere Rovers, in a move later extended to run until the end of the season. He made his professional debut on 17 March 2012 in a 1–1 draw at Sheffield United, and scored in his second appearance, a 2–0 win at Rochdale. In total, he scored five times in ten appearances.

Ahead of the 2012–13 season the striker renewed returned for a second loan period with Tranmere Rovers; a move which lasted until January 2013. He scored his first goals of his return with a hat-trick against Colchester United in a 4–0 win on 1 September 2012 that put Tranmere top of the league. Cassidy was then named the League One Player of the Month for September 2012, after scoring seven league goals during the month. He returned to Wolves after his loan spell ended in January 2013 having scored 11 goals in 26 appearances.

Cassidy made his Wolves debut as a substitute in the club’s FA Cup elimination at Luton Town on 5 January 2013, the final game of Ståle Solbakken’s reign, before being selected to start Wolves’ next league game by their new manager Dean Saunders. He made six league appearances as the club unsuccessfully fought to avoid relegation to League One.

In January 2014 joined Tranmere Rovers for a third loan spell, after a three-month deal was agreed. This loan spell, however, was less successful than his previous two as he scored just once in 19 appearances as the club struggled to avoid relegation.

After having signed a new one-year contract at Wolves (with an option for a further year), he was loaned to League One team Notts County in July 2014 until January 2015, during which time he scored four times during 20 appearances.

On 15 January 2015, he was loaned out for the rest of the season to League Two side Southend United. He won a play-off final promotion medal for Southend United.

On 23 June 2015, with effect from 1 July 2015, Jake signed a 2-year contract with a further 1 year option with Oldham Athletic.

On 31 August 2016, Cassidy had his contract mutually terminated by Oldham Athletic after 1 season at the club.

Cassidy signed for League Two club Stevenage for a five-figure fee on 14 January 2020. He was released at the end of the season.