The hire will see Montanaro reporting to Mark Rogers, head of investments at the boutique asset manager.
Montanaro previously spent over a decade at abrdn as an analyst, portfolio manager and most recently as an investment director.
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At abrdn, he was part of the portfolio construction team for the firm's flagship Emerging Markets ‘Long Term Quality' equity products, co-manager of the abrdn Emerging Markets Income Equity Fund and lead manager of a billion-pound EM segregated mandate.
Montanaro's father and the founder of Montanaro AM, Charles Montanaro, will remain chair of the firm and chair of its investment committee.
Cedric Durant des Aulnois, CEO, said: "I am delighted to welcome Adam to MAM. He joins at an exciting time for the business. Since launching the Montanaro Better World Fund in 2018, the company's global franchise has gone from strength to strength.
"Most recently, MAM has been nominated for 4 different Sustainable Investment Awards by Investment Week. The addition of Adam cements MAM's position as one of the best resourced investment teams in Global Small and MidCap."
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Adam Montanaro added: "I am thrilled to join such a talented, engaged and hungry team with so much success behind them and so much potential ahead.
"The quality growth investment philosophy I was imbued with at abrdn closely aligns with the philosophy at MAM and I look forward to contributing to the team".