Lighthouse Group has agreed a new contract with the Fire Brigades Union to be the preferred provider of financial advice to its members.
The contract will run for three years and under its terms Lighthouse will provide advice on savings, investments, pensions and protection, plus mortgages to FBU members.
Founded in 1918, FBU represents a membership of 36,000 fire service professionals, as well as 7,000 retired members.
Malcolm Streatfield, chief executive of Lighthouse, said: "The board is delighted that we have secured this partnership with the Fire Brigades Union, a new and exciting engagement for us.
“We look forward to developing our relationship over the coming years and working closely with FBU members, who themselves are dedicated to helping others, and to assisting them with their financial planning requirements.
“The board remains committed to increasing our affinity partnerships throughout the UK".
Lighthouse is the preferred financial adviser to 19 affinity partners with a combined membership of more than 6m people.
Dave Green, national officer of FBU, said: "We are pleased to have finalised this contract with Lighthouse.
“The new arrangements will enable our members to access invaluable financial planning assistance.
“Many find themselves in complex financial circumstances, and they will now be able to maximise opportunities they may not have known existed to secure their and their families' futures."
Earlier this year Lighthouse announced profits were up by 50 per cent for 2015, reaching £900,000.
Consolidator AFH made an aborted attempt to buy Lighthouse in March, which was rejected by the company's board.