The deal will see the combined entity renamed Janus Henderson Global Investors and hold a combined market capitalisation of 6 billion US dollars (£4.6 billion).
The two firms said their “merger of equals” will see cost savings of at least 110 million US dollars (£84.7 million) a year. Henderson and Janus shareholders are expected to own approximately 57% and 43% respectively.
The companies said on Monday: “Janus’ strength in the US markets will be combined with Henderson’s strength in the UK and European markets to create a truly global asset manager with a diverse geographic footprint which closely matches the global fund management industry.”
Henderson boss Andrew Formica and Janus chief executive Dick Weil will lead the new firm, which will apply for admission to trade on the New York Stock Exchange as its primary listing.
The deal, which still requires shareholder and regulatory approvals, has already received the blessing of Janus’s largest investor, Dai-ichi Life.
The combined firm will have around 2,300 employees across 29 locations around the world, with revenues of 2.2 billion US dollars (£1.7 billion) and underlying earnings of 700 million US dollars (£539 million).