Pick Everard managing partner David Brunton said the deal - the value of which has not been disclosed - would allow Pick Everard to expand its base in the East Midlands and London markets.
Established in Leicester in 1866, Pick Everard employs around 300 architects, engineers and project managers in offices throughout the UK and in Ireland. It ahd a turnover of £19 million by the year-ending April 2007.
Rothera Goodwin has a staff of 15 and clients including Honda and Pendragon. Its turnover by year ending March 2007 was £750,000.
Brunton said that he expected the merged firm to increase total turnover by 25 per cent in five years.
In a statement, Rothera Goodwin directors Paul Rothera and Ian Goodwin welcomed the acquisition and claimed it would provide an 'opportunity to offer comprehensive multi-disciplinary design services to clients.'
The firm will continue to trade as Rothera Goodwin and there will be no changes to the current management team.
Brunton added: 'Both practices have similar values and aspirations. We look forward to building on Rothera Goodwin's successful history and established reputation and to strengthening our position in the region.'