Clients representing over 90 per cent of Geneva's assets under management agreed to the transaction, which was first announced in June.

Henderson’s North American business now has around $18.3 billion in AuM, representing around 15 per cent of group assets. The move doubles Henderson's number of US-based investment professionals and quadruples its US institutional AuM to some $8 billion. 

Nicholas Bauer, who is responsible for Geneva's distribution, will now head US institutional distribution as part of an integrated team reporting to Chuck Thompson, head of North American distribution.

Founded in 1987, Geneva Capital Management has $5.4 billion in AuM as of September 30, 2014, with a 25-strong team including 11 investment professionals. Going forward the firm's philosophy will remain the same and it will continue to operate from Milwaukee, WI.

Geneva's client base includes institutional investors and high net worth individuals. The firm also acts as a sub-advisor to a number of third-party mutual funds.