The group, which has operations in 100 countries throughout Europe, America, Asia, the Middle East and Africa, has grown consistently since 1999, when it made sales worth £195m.
The firm said its recent growth was partly the result of its May 2002 merger with Franklin + Andrews, the QS and project manager.
The figures also reflect Mott's purchase last year of two niche firms. It bought health consultant HLSP Group for £7.3m in October and GRC Consultants, a biochemical and pharmaceutical designer, in July.
Mike Blackburn, the chairman of Mott MacDonald, said the company was interested in making further acquisitions. He said: "We will be looking for niche consultancies in the UK as well as possible geographic expansion."
Franklin + Andrews is now part of the group's management economics and consultancy division. After a poor performance in 2002, last year's turnover was up 40% and profit was "back to normal".
In his first chairman's statement since taking over from Tim Thirlwall at the start of the year, Blackburn described 2003 as "a successful year – one of considerable change and material growth".
The firm admits that prospects for its main geographical regions are patchy: the UK is increasingly competitive, question marks remain over recovery in the USA and Hong Kong is, at best, challenging.
On the other hand, Ireland and Asia have shown some signs of recovery.
However, Blackburn added that the firm may have "turned the corner" in America, as it had won a contract for the extension of a rapid transport system in California with Bechtel.
Keith Howells, the group managing director, said: "Contracted workload for 2005 is weaker than it was for 2004 at this time last year, indicating changing markets and a need to maintain our drive to win work."
According to the chairman's statement, the firm employed an average of 6850 staff in 2003.
It has taken steps to standardise its IT systems and business procedures worldwide, and a new management information system has been rolled out across the globe.