Freshfields Bruckhaus Deringer and Skadden Arps Slate Meagher & Flom are leading on the $6bn (£4.6bn) merger of investment firms Henderson Group and Janus Capital.

Freshfields is acting for longstanding client Henderson, which is headquartered in London, while Skadden is advising New York-listed Janus.

The deal, which will be structured as a share-for-share exchange, will see the combined group renamed Janus Henderson Global Investors and co-led by the CEOs of Henderson and Janus.

The new entity will de-list in London and apply for listing on the New York Stock Exchange. It will have approximately $320bn of assets under management.

The Freshfields team is being led from the UK by London corporate managing partner Simon Marchant and corporate partner Oliver Lazenby, and from New York by global M&A co-head Peter Lyons and US corporate head Matthew Herman.

Marchant said: "This is exactly the sort of complex, cross-border transaction which underscores the importance of having a fully integrated, top-tier international M&A practice."

Skadden is fielding a team led by London corporate partners Michael Hatchard and Scott Hopkins, alongside New York corporate partner Ralph Arditi and New York-based financial institutions partner David Hepp.

It is the second recent deal that Freshfields and Skadden have both worked on, having both won roles on Deutsche Bank's £935m sale of Abbey Life to Phoenix Group, which was announced last week.

Skadden acted for Phoenix with a London team led by corporate and insurance partner Robert Stirling, M&A partner Linda Davies, corporate finance partner Danny Tricot and tax partner James Anderson. Freshfields advised Phoenix on the debt aspects of the deal with a team led by London banking partner Sean Pierce, who is also co-head of the firm's global financial services sector group.