Morrison was appointed captain of Cardiff in September 2016 and helped the club win promotion to the Premier League in the following campaign after finishing as runners-up in the Championship during the 2017–18 season.

[10] The following season, Morrison featured more frequently in the first team, making 23 appearances in all competitions and scored his first goal for the club on 25 October 2008, in a 2–0 league victory against Oldham Athletic.

[14] Having struggled to break into the first team at the start of the 2009–10 season, with Gordon Greer and Scott Cuthbert being preferred,[6] Morrison signed a one-month loan deal with Southend United on 14 November 2009.

[22] Having displaced Lecsinel Jean-François in defence,[6][23] Morrison scored five times in the first half of the season, including a goal against his former club Plymouth in the FA Cup.

[24] On 14 January 2011, Swindon Town and Reading reached an agreement to transfer Morrison after a release clause in the player's contract was activated,[25] with the deal completing four days later.

[3][27] Having failed to make an appearance for the club since signing, on 23 March 2011, he joined Huddersfield Town on loan until the end of the season, with Reading retaining 24-hour recall after the first month.

[30][31] Despite never playing for the club, Huddersfield manager Lee Clark commented that he was "gutted" to lose Morrison, describing him as "a very good footballer and has shown a terrific attitude all the time.

"[32] He made his Reading debut in a 2–1 defeat against Charlton Athletic in the second round of the League Cup on 23 August 2011, scoring a consolation goal in his first appearance for the club.

[37] He played in both legs of the club's 3–2 semifinal aggregate victory over Milton Keynes Dons and scored in the play-off final penalty shoot-out against Sheffield United, which Huddersfield won,[37] promoting them to the Championship.

[39] After returning to Reading, Morrison's first appearance in the 2012–13 season came in a 3–2 League Cup victory over Queens Park Rangers (QPR) on 26 September where he came on as a second-half substitute.

[41] He made his Premier League debut against QPR on 4 November 2012,[42] helping the side record their first clean sheet of the season in their following match, a 0–0 draw with Norwich City.

[44] After dropping out of the side midway through the season, Morrison finished the campaign in a defensive partnership alongside Adrian Mariappa under new manager Nigel Adkins.

[51] On 15 August 2014, Morrison signed a four-year contract with fellow Championship side Cardiff City for an initial fee of £3 million, with further add-ons based on appearances and future promotions.

[57] Morrison was ever-present in Cardiff's starting eleven before suffering a knee injury during a 1–0 loss to Birmingham City on 19 December 2015, which was initially expected to rule him out for a month.

[68] In February, Morrison scored three goals in five games, as well as helping his side record three clean sheets, which led to him being nominated for EFL Championship Player of the Month.

[72] Morrison suffered a broken nose during a 2–1 victory over Brighton & Hove Albion in November 2018 but rejected the chance to have surgery to rectify the injury, instead choosing to postpone the operation in order to keep playing.

[76] He remained sidelined for six weeks, before making his return in a 5–1 defeat to Watford on 22 February, and finished the season with 35 appearances in all competitions as Cardiff suffered relegation to the Championship.