Mangan was heavily linked with a return to Hyde the following season, but he rejected them in favour of a full-time contract with Conference Premier side Accrington Stanley, after impressing during the club's pre-season schedule.

[5] After making his debut in a 1–0 win over Canvey Island on 13 August 2005,[6] Mangan scored his first goal for the club in his third appearance during a 3–1 defeat to Cambridge United.

His goals helped Accrington gain promotion to The Football League at the end of the 2005–06 season; the first time the club had achieved this in 50 years.

At the end of the 2006–07 season, Mangan was offered a two-year deal by Accrington, but rejected it in favour of League Two side Bury, having appeared in a pre-season friendly for the club against Everton.

He was injured at the beginning of December 2007 with a suspected hernia problem and later underwent surgery, restricting him to just six appearances in the rest of the season as he struggled to regain fitness.

Following the sacking of Bury manager Chris Casper, Mangan was allowed to return to Accrington Stanley by his replacement Alan Knill on a one-month loan deal, scoring one goal in seven appearances.

[12] It was at Forest Green that Mangan's goalscoring reputation began to form; his first season saw him finish as the league's top scorer with 26 goals in 41 games.

Mangan started the next season in an unfamiliar left-wing position; despite this he still finished as the club's top scorer with 16 league goals, helping them to the play-offs, where they lost to Luton Town.

[30] By the end of October 2014, Mangan was joint top scorer at Shrewsbury, alongside James Collins, having scored six goals in all competitions.

[32] He marked his first start since November by scoring a brace and providing an assist in a 3–0 home win against Hartlepool United on 17 January 2015, to help move Shrewsbury back into the League Two automatic promotion places.

[33] Shrewsbury were subsequently promoted back to League One at the first attempt, following a 1–0 away win at Cheltenham Town in April 2015,[34] however due to Financial Fair Play restrictions, they were unable to offer Mangan an extension to his contract.

[36] He scored seven goals in the first half of the season, including five in four matches during September and October, but lost his place in the team due to injury and manager Gary Brabin's subsequent tactical switch to a 4–5–1 formation with James Norwood preferred in the lone strikers role.

[38] He made his return debut in an FA Cup tie away at Cardiff City three days later, scoring the only goal in a 1–0 victory, sending Shrewsbury through to the fourth-round for the first time since 2002–03.

[39] He missed a penalty on his home return against Barnsley,[40] but scored a second-half equaliser at Burton Albion the following week, with Shrewsbury going on to win 2–1 at the league leaders.

On 4 November 2023, during a 7-2 win in an FA Cup first round tie against Whitby Town, Mangan gave Ollie Dewsbury his senior debut, bringing him on as a substitute in the 87th minute.