Lighthouse was already the largest quoted adviser firm in the market, with Sumus the second largest.
The new group will have a turnover in excess of £80m, estimated assets of £22m and around 900 advisers.
Lighthouse chairman David Hickey says the Sumus, Falcon, FSAS and Lighthouse brands will all remain in the long-term due to the goodwill the names have built up.
Lighthouse Group will acquire the shares of Sumus although the corporate brand of the new entity has yet to be decided.
Hickey will become executive chairman of the new firm with Sumus chief executive Allan Rosengren and Lighthouse chief executive Malcolm Streatfield sharing joint chief executive roles.
Rosengren will focus on external relationships with providers and Streatfield on internal operations.
Falcon finance director Peter Smith will become group finance director.
Julian Telling, one of the founders of Falcon, is to leave the firm along with Sumus chairman Paul Bradshaw. Telling will remain the fourth biggest shareholder in the new firm and work as an introducer to it.
Lighthouse executive director John Stevenson, who joined the board when Lighthouse acquired Carrwood Group in 2005, and non-executive director Philip Whitehead will both be leaving.
Rosengren will be the largest shareholder in the new firm, with 15 per cent, followed by the Lighthouse board, with 7 per cent, LV= with 6 per cent and then Telling with 5 per cent.
Hickey says he made an initial call to Sumus in December which was followed up by a meeting in January where it became clear the two firms where a good match.
He says: “Both firms are profitable, have cash available and are not financed by debt, offering advisers a security that is not available in other parts of the market.
We are not controlled by a product provider or a small group of providers and operate and trade completely independently. Not many others can stand up to these tests.”
Hickey says the new entity will continue with its goal of turning assets under advice into assets under management and will be looking to secure new deals with fund managers on the back of its increased scale.
Falcon currently operates its Brunel funds, outsourced to Premier Asset Management, and Lighthouse offers F&C’s lifestyle funds.
Sumus chief executive Allan Rosengren says: “It fulfills a number of key objectives in terms of achieving meaningful size, scale and geographic coverage, whilst further broadening the range of services offered to IFAs and clients.
‘We are enormously enthused by it and believe it to be in the best interests of all stakeholders in both Sumus and Lighthouse. Once effected, we look forward to being part of a larger group with all of the businesses in the group maintaining their individual identities but working together, to mutual advantage and the benefit of clients in the years ahead.’