MGIM said the combined business would create a strong foundation on which to accelerate its growth as an investment provider to the UK adviser market.
Seneca’s chief executive David Thomas said the deal added value to all parties as it built scale whilst maintaining the “nimbleness and dynamism” of a boutique.
The deal is subject to regulatory approval and no redundancies are expected as a result of the deal.
Both companies are multi-asset management fund houses. The Seneca funds will assume the MGIM brand.
Ferdi van Heerden, chief executive of MGIM, said: “This is a very exciting acquisition. The two teams complement each other well and have a strong cultural fit.
“The acquisition will enable MGIM to meet the growing demand for multi-asset investment solutions from advisers, discretionary fund managers and their clients.”
The asset management industry has seen a considerable increase in M&A activity over the past few years with some of the biggest deals including Jupiter’s takeover of Merian Global Investors earlier this year and last year’s £6.6bn merger between Premier and Milton.