Stephens, an American financial services firm, is set to take a minority ownership stake in CRUX Asset Management.
Subject to FCA approval, Stephens will hold approximately 20% of CRUX share capital, with new ordinary shares issued to support the deal.
John Stephens, who is currently a senior vice president with Stephens' affiliate Stephens Inc, will join the CRUX board as a non-executive director.
Stephens is based in Little Rock, Arkansas, with a European practice in the UK and Germany. Founded in 1933, the firm is one of the largest privately owned investment banks in the United States.
Karen Zachary (pictured), CEO at CRUX, said on the deal: "This is a very exciting strategic step for CRUX and we are delighted to be partnering with a firm of such a high calibre as Stephens and see clear synergies between our two firms.
"Over the last five years, we have built a scalable platform at CRUX that has enabled us to expand our investment offering into Asia and the UK with complementary strategies that fit our plans to build a diversified range of active management strategies."
John Stephens at the firm added: "We are excited to make an investment in CRUX Asset Management which, in our view, is comprised of extremely talented individuals who come together to create a cohesive and exciting team with a bright future.
"We are looking forward to working with Karen and others in helping the business achieve its goal of becoming a leading, independent asset manager and the platform of choice for high quality PMs with a passion for what they do."
Last month, UBP and CRUX entered a strategic partnership with a focus on Asia, as CRUX said it would advise UBP on its Asia equity funds and mandates, while UBP will provide investors based in Asia with "exclusive" access to CRUX's equity products.