Garthwaite, presently at electronic components and industrial products firm Premier Farnell, will be responsible for Atkins' group comms, marketing and IR when he starts in August.
The company is working on London's Olympic Park for 2012, as well as the development of medium-weight armoured vehicles for the Ministry of Defence.
‘James's hire is part of a restructuring of the group executive to help drive international expansion,' said Atkins CEO Keith Clark. ‘The creation of this group-level role will help us co-ordinate internal and external comms as we grow.'
Garthwaite joined Premier Farnell in 2004 as group director of comms, replacing the retiring Nick Ross.
At the firm he heads external comms and IR, as well as internal comms for the company's 5,000 staff.
Prior to Premier Farnell, Garthwaite spent seven years with Brunswick. His career began in the City in 1985 with Cazenove & Co, where he spent four years in equity research and fund management.
Atkins posted impressive earnings in the year to 31 March, up over £20m on the previous year.
It benefited from winning an order to help design road, bridge and water systems for the 2012 Olympics, and said demand from Network Rail picked up during the second half of last year.