MacLennan, the managing director at Associated Newspapers, is the Barclay brothers' first senior hiring since they bought the Daily and Sunday Telegraph.
The Associated chairman, Lord Rothermere, acted swiftly to replace MacLennan with Kevin Beatty, the 46-year-old managing director of its regional newspaper division, Northcliffe Newspapers.
Paul Thomas, a managing partner at MindShare, said of MacLennan: "He's got a strong track record at Associated but this could prove to be a new challenge. The Telegraph is a profitable company but he'll face numerous challenges with compacts and competition from Rupert Murdoch. The paper now has the opportunity to establish itself as the brand leader it is."
MacLennan, 55, was heavily involved in Associated's aborted bid for the Telegraph Group. During his ten years at the helm of Associated Newspapers, he has overseen its move into new media, the launch of Metro and its success with Loot. He replaces Jeremy Deedes at the Telegraph Group. Deedes is retiring after returning to the Telegraph Group on an interim basis while its sale was completed.
Guy Zitter, the managing director of the Daily Mail who was recently handed the additional role of group commercial director at Associated, was previously seen as a possible successor to MacLennan.
Michael Pelosi, the deputy managing director at Northcliffe, replaces Beatty in the managing director's role at the regional group.