McLellan was sports editor of the North-West Evening Mail and Assistant Editor of The Journal, Newcastle, before joining The Scotsman Publications in 1994 and had two spells editing the Edinburgh Evening News (1997–2002 and 2004–2009) and also edited Scotland on Sunday (2002–2004).
Johnston Press appointed McLellan to editor of The Scotsman on 20 February 2009 following the departure of Mike Gilson, and a month later also in May 2009 appointed editor-in-chief of The Scotsman Publications.
McLellan was dismissed by Johnston Press on 12 April 2012 as editor of The Scotsman in a management restructuring process which involved the scrapping of the editor-in-chief role with the editors of each title reporting directly to the managing director of the Scottish Publishing Unit Andrew Richardson. He was replaced by Ian Stewart, who remained editor of its sister title Scotland on Sunday.
On 23 June 2012 McLellan was appointed director of communications of the Scottish Conservatives. Former Tory spin doctor Ramsay Jones was suspended during the previous year's party leadership elections. McLellan advised Scottish Tory leader Ruth Davidson on communications strategy, direction and content.
On 28 June 2013 the Scottish Conservatives announced that McLellan had chosen to resign his post as the party's communications director and would take up the role of director of the Scottish Newspaper Society  in September.
In the May 2017 Scottish local government elections McLellan was elected to the City of Edinburgh Council as Conservative councillor, one of four councillors for the Craigentinny & Duddingston Ward.
He was a member of the Press Complaints Commission (2008-2012), the Defence, Press and Broadcasting Advisory Committee (2006–12) and was twice chair of the Scottish Newspaper Society's editors' committee.
- Michael Crow (journalist), Director of Strategy and Communications for the Scottish Conservative Party, 2009–2010
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- "Arts and Humanities | About". University of Stirling. Retrieved 9 September 2020.