The appointment means Marchant, who stepped down from the Perth-based utility in July after ten years in charge, will be the chair of two listed firms, having joined renewable energy specialist Infinis last year.
He is also a non-executive director at Glasgow-based generator supplier Aggreko and at privately-owned Cyberhawk, an operator of unmanned aerial vehicles based in Livingston.
Marchant has been on Wood Group’s board since 2006 and became senior independent director in May 2012. He is due to step up to the chairman’s role in May, when Langlands retires at the end of the firm’s annual shareholder meeting.
Langlands joined Aberdeen-based Wood Group as finance director in 1991, and nine years later became deputy chief executive. He has twice succeeded Sir Ian Wood in the company’s two top roles – first as chief executive in 2007, and then as chairman in November 2012 when Wood retired after 30 years in the post.
Wood Group, which employs about 44,000 people around the world, is currently run by Bob Keiller, who took over chief executive from Langlands.
Marchant said: “My board colleagues and I wish Allister every happiness in his retirement and I look forward to working with Bob and his executive team in the next phase of the group’s development.”
Wood Group is due to publish its annual results on 18 February. The firm warned in December that earnings at its engineering division could fall by about 15 per cent this year because of project delays and weakness in the Canadian market, but demand from the US shale gas industry has helped performance at its PSN division, previously run by Keiller.