Midlands law firm Gateley Wareing and Scottish solicitors Henderson Boyd Jackson have confirmed the completion of their merger.
First announced in October, the new firm will be called HBJ Gateley Wareing.
It will have 58 partners, 230 fee earners, a total staff of 390 and offices in Birmingham, Edinburgh, Glasgow, Leicester and Nottingham.
It will immediately move into the top 60 UK law firms.
The firm anticipates fee income in excess of £29 million in its first full financial year.
It will be led by a management board comprising senior partners Malcolm McPherson and Mike Ward, finance director Martyn Finnigan, chief executive Stewart McIntyre, and partners Fraser Jackson and Andrew Madden.
HBJ Gateley Wareing represents financial institutions, major corporates and mid market companies across a broad range of industry sectors as well as private individuals.
The firm's core practice areas include banking and finance, corporate and commercial, employment, construction, litigation and dispute resolution, commercial and residential real estate, tax and private client services, shipping and transport.
The rationale for the merger lies in the two firms' significant growth in the last few years, and their increased expertise in advising large national corporations, banks and financial institutions.
The firm's strategy will be to further develop in England and Scotland.
Mr Ward said "To have a merger agreed and completed in such a tight timescale is testament to the remarkably similar cultural outlook, management style and a shared view of excellence of both firms.
"We have each experienced high levels of growth in our respective regions and believe the merger will allow us to translate this, with an evolutionary and integrated approach to growth, into a strong national platform."
Mr McPherson added "The decision to merge the two firms could not have come at a better time.
"We are committed to expanding our operations throughout the UK, and welcomed the opportunity to leverage our undoubted strengths especially in financial services and banking."