Merian Global is owned by Boston-based private-equity firm TA Associates Management, which acquired Merian in 2018 from Old Mutual Ltd., the South African financial services conglomerate.
The acquisition brings Jupiter another £22.4bn of actively-managed assets taking its total assets under administration to more than £65bn.
The British fund manager will make a payment of 370 million pounds ($482 million) through the issue of new Jupiter stock to Merian shareholders, with an additional deferred performance payout, according to a statement on Monday.
"Our substantial stake in the combined firm underlines our belief that this transaction will deliver significant strategic benefits and returns to shareholders". Outflows during 2019 were 4.5 billion pounds. Merian was founded by Richard Buxton, who led the buyout from Old Mutual but who subsequently stepped down as CEO in January of past year.
"Ultimately, Jupiter is unlikely to do anything to disrupt the successful Merian teams, particularly the renowned United Kingdom equities offering".
The acquisition will diversify Jupiter's existing business, with its current top five funds falling from 46% of AUM to 33% of the AUM of the new enlarged group.
Fundcalibre managing director Darius McDermott said while the reports were surprising, there has been a growing trend of consolidation in asset management for the last decade. He became co-chief executive of the merged group alongside Dick Weil before leaving a year later after the board chose Weil as the sole CEO.
Miller continued: "In terms of investment teams there is little overlap so this is fairly complementary from that point of view".
The deal is the latest among actively run fund managers, which are facing rising regulatory costs and pressure on fees as more investors turn to passive funds aiming to do no more than track the makeup of a benchmark index such as the FTSE 100.
Jupiter will take on around 29 million pounds of Merian debt and will also pay a further 20 million pounds to Merian shareholders if certain targets are hit.