Wallis started his career in the industry following the completion of an electrical apprenticeship with Drake & Skull.
He has held director level roles in a number of companies, including Laing O’Rourke, Skanska and Mace, before moving to London-based Phoenix ME in 2018.
In his new role at MD in the south, Wallis will be part of the group executive leadership team, reporting directly to CEO Gareth Simm.
His predecessor, John Lennie, moves into a new role as group executive director.
Simm said: “Marcus has an exceptional capability. He has years of operational experience and leadership and is well known and, well liked, across the industry.
“We look forward to him demonstrating his skills and experience and to watching our southern business flourish under his watch.
“Part of that will be to grow our London business to become a leader in the southern regions of the country, not just in the capital.”