[5] After impressing in a three-day trial with Sunderland in November 2004, Welsh signed with the club for £15,000, and could have included a compensation for amount of time on the field stipulation to £35,000.
Upon signing for Sunderland he was assigned the vacant number 11 shirt, and made his club debut on 1 January 2005 in a 3–2 defeat to Preston North End, replacing Marcus Stewart in the 68th minute.
After Sunderland's promotion to the Premier League, Welsh retained the number 11 shirt, starting the season in place of injured defender George McCartney.
Following the transfer of popular midfielder Julio Arca to Middlesbrough in the summer, Welsh was expected to start the season as first choice winger, however injury hit early on in pre-season.
Welsh picked up an injury during a pre-season win against League of Ireland club, Shelbourne, prompting Quinn and new manager Roy Keane to sign Swedish winger Tobias Hysen and Celtic midfielder Ross Wallace to fill the left-midfield role.
Welsh subsequently re-joined Leicester on loan when he regained fitness, although he managed only four league starts for them, and returned to Sunderland in the New Year.
[7] On 16 May 2007, Welsh scored his first goal for Toronto in a rain soaked 1–0 home win over defending MLS champions, Houston Dynamo.
[14] Welsh played 38 games for Yeovil in his first season,[15] becoming a fans' favourite when the team went on a four-game winning streak scoring four goals direct from his set pieces.
He secured Yeovil's league one status for another season with an 85th-minute equaliser at home to Oldham Athletic the day after his first child was born.
On 29 July 2020, Welsh was selected from 750 applicants to become the first manager of Bury AFC,[23] but the first season was ended prematurely due to the COVID-19 pandemic.
[24] Welsh led Bury to the title; the side finished 11 points clear, winning 27 out of 36 games, boasting the highest goals total and best defensive record in the division.