Isgrove was a member of Southampton's academy system; his first inclusion in the Southampton's first team came on 30 October 2012 in the fourth round of the 2012–13 League Cup against Leeds United, for which he was included on the bench. The midfielder came on as a substitute for winger Steve De Ridder in the 67th minute, seeing out the last 23 minutes of the 3–0 defeat. He made his first start for the club the following August in a 5–1 victory against Barnsley in the League Cup second round, setting up the opening goal.
Isgrove made his league debut for Southampton in the first game of the 2014–15 season, playing the last 8 minutes of a 2–1 loss at Liverpool in place of Steven Davis.
On 17 March 2015, it was announced that Isgrove has signed a two-year contract extension until 2017 at Southampton. He was released by Southampton at the end of the 2016–17 season.
On 13 March 2014, Isgrove joined League One side Peterborough United on a one-month loan deal, subsequently extended to the end of the season.
Isgrove also played in the 2014 Football League Trophy Final, in which Peterborough won 3-1 against Chesterfield on the 30 March 2014 at Wembley Stadium in London. Isgrove returned to Southampton after his loan with Peterborough ended.
On 18 March 2015, Isgrove signed an emergency loan deal with Sheffield Wednesday until the end of the season. Isgrove made eight appearances for Sheffield Wednesday, before he returned to Southampton.
On 24 October 2015, Isgrove completed a loan move to League One club Barnsley where he stayed until the end of the season.
Isgrove helped Barnsley win the Football League Trophy after beating Oxford United of League Two, a 3-2 win in the final on the 3 April 2016 at Wembley Stadium.
Isgrove returned to Wembley on the 29 May 2016 with Barnsley for the Football League One play-offs final. Barnsley won the match after beating Millwall 3–1 in the Play-Off final, in which Isgrove scored his first goal for Barnsley in the 74th minute. Barnsley gained promotion to the Championship, and Isgrove returned to Southampton at the end of the season, when his loan with Barnsley ended.
Championship club, Barnsley confirmed on 2 July 2017, that Isgrove has signed a three year contract at the club.
In January 2013 he was selected for the Wales under-21 squad and made his debut in a 3–0 win against Iceland in a friendly match on 6 February 2013.
He made his senior international début on 24 March 2016 as a 62nd-minute substitute in a friendly against Northern Ireland helping Wales to a 1–1 draw.As of match played 28 January 2017
Football League Trophy: 2013–14.
Football League Trophy: 2015–16.
Football League One play-offs: 2015–16.
EFL Cup runners-up: 2016–17