Squires, currently chief operating officer at rival firm Cobham, will join the Senior board as group chief executive-designate on 1 May, and will take on the group chief executive role on 1 June, when Mark Rollins stands down.
Rollins, who announced his retirement in August 2014, has been with the firm for 17 years.
Senior chairman Charles Berry commented: “David clearly has the depth and breadth of experience, and the personality and drive, to lead Senior through the next stage of its development. I am confident that Senior will continue to make strong progress under his leadership.”
He added: “Mark Rollins has made an enormous contribution to Senior in a career spanning 17 years. Accordingly, on behalf of the board, I would like to thank him for his dedicated and successful service.”