Leslie's first broadcasting experience was with London radio station Capital Gold, working initially as a football reporter and secondary commentator before taking the lead role on Jonathan Pearce's departure to the BBC in 2002.
Leslie transferred to Sky in 2003, initially to work on coverage of the UEFA Champions League and soon after helped launch Football First in 2004.
Following the departure of Ian Crocker to Setanta Sports in the summer of 2006, Leslie took over the role as Sky's principal commentator on the Football League.
Leslie's live Premier League debut for the Sky Sports corporation came in the clash between Birmingham City and Aston Villa in the 2004–2005 season.
Leslie can now most often be heard as lead commentator on Sky Sports coverage of the Premier League or EFL Championship.