Burness, the ambitious central belt law firm, has pulled off a marriage with Aberdeen market leader Paull & Williamsons to create the biggest all-Scottish legal merger and one of a new 'big two' in Scotland.

The firms' principals say the deal contrasts positively with other recent consolidation activity in the sector, which has seen the loss of independence for McGrigors and aborted English mergers by two of the other 'big four' firms.

Burness Paull & Williamsons will have 400 staff including 60 partners and 158 lawyers, ranking it alongside Brodies as one of the two largest firms measured on Scottish resources and turnover.

Philip Rodney, the Burness chairman who will lead the combined firm from December 1, said: "The merger will create a firm with established offices of similar size in Aberdeen, Edinburgh and Glasgow.

"The new firm will hold an unparalleled position in the Scottish legal landscape by virtue of the quality, depth, expertise and balance of its resources across the three cities."

Mr Rodney said both firms had decided "not to try and be bit players in London", adding: "All the firms around us have been rushing into a different type of merger with an English practice.

"The disadvantage of that is that firms end up as branch offices of mid-market English firms – this effectively gives independence through merger – and it is not one that anyone else can replicate."

Both firms drew 20% of turnover from overseas, Mr Rodney said, with Burness winning strong referral business from City firms and foraging into Italy, Germany, the US and Canada.

The north-east firm had "dominated the Aberdeen market for the past 40 years" but had wanted to widen its offering into areas such as listed companies and private equity.

Scott Allan, managing partner at Paul and Williamsons, said: "Both firms have had several approaches to merge in the past, but it is hard to imagine a better fit.

"Our culture, ambitions and focus on quality are shared, our geography, clients and expertise are complementary and our combined objective, to be the leading Scottish commercial law firm serving Scottish, UK and international clients in and from Scotland, reflects our common ethos.

"Our international credentials are strong and present significant potential for the merged business."

Norway, Brazil, the Middle East and the US are active markets for the Aberdeen firm's oil and gas team.

Mr Rodney will become chairman and his managing partner Ian Wattie will hold onto the same role in the new entity, with Mr Allan as his deputy and the Aberdeen firm's chairman Gordon Buchan as a consultant.

But Mr Rodney insisted there would be "a good balance" between the firms in the allocation of new director and divisional roles.

He said:"The only precondition was that it must be a real merger and not a takeover – where any firm has simply taken over another two plus two has made four, you need two strong firms to create something new and even better."

Burness last month reported a 4% rise in turnover to £24.3m and a 6% uplift in profits to £11.1m last year, while some bigger rivals retrenched.

The business has grown 25% since 2009, driven by its corporate finance, funds, and commercial dispute resolution teams.

Paull & Williamsons saw turnover flatlining at around £13m last year but has moved back into growth, while profitability is said to match Burness at around 45% of revenue.

Burness was the third most profitable firm per equity partner in 2011, according to Legal Business, generating £372,000 per partner, just ahead of Brodies and behind niche operators Dickson Minto and Turcan Connell.