The move will see a managed exit from the Glasgow business for founder Brian McKenna.
While Mr McKenna, 65, will step back from giving financial advice he is being retained for a two-year consultancy period. His business partners Nigel Walker and Jon Sweeney are remaining in the business under the Bellpenny brand.
MGW is understood to have in the region of £180 million of assets under management and administration. Its client base is mainly in central Scotland with a small number in and around Aberdeen.
Mr McKenna, who has been running the business for 27 years, said: "The important thing was to get a deal where the people coming in would continue to look after the clients in the right way. We have had various overtures down the years but we only really started thinking seriously about it in the summer when we appointed an agent [to help us look at selling].
"It's time for me to hang up my boots but I have a nice two-year period when I will be around as a consultant but not actively giving advice."
The deal is Bellpenny's 13th since it received regulatory approval last October and it now has £1.25 billion of funds under management. In August it bought KM Financial Advisers in Glasgow.
Bellpenny chief executive Kevin Ronaldson said: "It's a testimony to the energy and professionalism of the whole Bellpenny team that we've been able to sustain such strong deal-making momentum, while also maintaining our operational rigour and strong service ethic on behalf of a rapidly-growing client base."