He is a civil engineer with extensive experience in the design of ports, harbours and coastal work.
Blackburn also ran Mott's Hong Kong arm, Mott Connell, between 1994 and 1996. During this time he headed up the firm's £5bn portfolio of work at Hong Kong airport.
Thirlwall retires after 38 years' service with the firm, including the last five as chairman. During his half-decade at the helm, the group's turnover doubled and staff numbers increased 70%.
Keith Howells, formerly Mott's head of worldwide business in water and the environment, has taken over as group managing director.