On 7 May 2014, O'Carroll was confirmed to have left Cliftonville after winning back to back league titles and league cups. He then joined
Crusaders, signing a two-year pre-contract for the club. During his time at Crusaders as a semi-professional player, O'Carroll was also appointed manager of
Crusaders Newtownabbey Strikers in April 2015 (left in January 2017). On the expiration of this contract, Diarmuid had won 4 back to back titles with 2 clubs and then O'Carroll decided to retire from football to focus on coaching. On 23 November 2018, O'Carroll came out of retirement, signing a short-term deal at Dungannon Swifts. O'Carroll has completed a number of coaching badges and has a long-term ambition of pursuing this area after he retires from playing. On 27 February 2019, he was appointed manager of
Glentoran Women. He left the position in June 2019, to become the Director of Coaching for Downtown Las Vegas Soccer Club. On 23 September 2019 he took over the role of coach to
Motherwell FC's Under 18s. This was a post that had briefly been filled by Darren O'Dea who had moved on to coach the under 18s with Celtic. On 7 June 2021, O'Carroll joined
Morecambe as a first-team coach, joining
Stephen Robinson after they had worked together at Motherwell. On 9 January 2022, O'Carroll took charge of Morecambe in a 3-1
FA Cup defeat to
Tottenham Hotspur, after manager Stephen Robinson tested positive for COVID-19 on the eve of the match. On 22 February 2022, O'Carroll was appointed as Robinson's assistant manager at
St Mirren. On 13 March 2023, O'Carroll joined
Michael O'Neill's backroom staff with the
Northern Ireland national team as a senior coach, whilst remaining in his assistant manager role at St. Mirren. On 16 June 2025, O'Carroll was appointed as
Brian Priske's assistant manager at
Sparta Prague. == International career ==