The company will acquire the stake from Rosemont Partners III, a closed private equity fund managed by Rosemont Investment Partners.
The financial terms of the deal were not disclosed.
Founded in 2003, Boston Common is an equity manager dedicated to integrated environmental, social, and governance (ESG) impact investing.
As of 31 December 2020, the company had around $3.9bn in assets under management.
AMG president and CEO Jay C. Horgen said: “We have deep respect for Boston Common’s consistent investment process, strong long-term track record, and extraordinary expertise in sustainable investing.
“Geeta Aiyer, founder of the firm, has been recognised as a leader in ESG and impact investing for more than 30 years. AMG’s partnership with Boston Common further enhances our strategic participation in ESG investing, an area that is one of the fastest-growing segments in the investment industry, and an increasingly significant focus for clients globally.”
Boston Common CEO Ally McDonald said: “We believe that AMG’s distribution platform and relationships with global asset owners will meaningfully enhance the growth of Boston Common’s integrated ESG capabilities and further diversify our client base.
“AMG’s collaborative partnership approach will support our efforts to address climate change, racial and gender inequity, and corporate governance as we enter the next phase of our growth and continue to build an enduring, multi-generational, independent investment firm.”