The contract could be worth as much as £1m a year to Morgan Cole.
Eversheds has acted as chief adviser to the National Assembly since its inception in 1999. Morgan Cole was restricted to carrying out conflict work during that time, but when the contract was put out to tender again, it snatched the main role.
It will work with the assembly's in-house legal team led by Counsel General Winston Roddick QC. The contract includes employment, dispute management and land and highways work. The firm will also advise client divisions undertaking functions in relation to the fields of responsibility exercised by the assembly.
Morgan Cole's Cardiff senior partner Guy Clarke said: “This is a highly significant and prestigious appointment for us and we're delighted to have been appointed, particularly given the rigour of the selection process.”
Insiders will be hoping that the contract will help Morgan Cole turn the corner after losing a high proportion of its partners since the 1998 merger of Welsh giant Morgan Bruce and Thames Valley firm Cole & Cole.