Janus Henderson has received a takeover bid from Nelson Peltz's hedge fund five years after the activist investor first disclosed a stake in the US asset manager.

Trian Fund Management has joined forces with General Catalyst to offer $46 a share in cash for Janus Henderson, valuing it at $7bn. Shares soared more than 16 per cent in New York on Monday.

Trian and related parties already have an interest in about a fifth of Janus Henderson's stock. Peltz and General Catalyst chief executive Hemant Taneja said in a letter that a deal would "de-risk an investment that we believe is highly sensitive to capital market and geopolitical dynamics".

The offer price was a 56 per cent premium to where the shares were trading as recently as April when markets conditions were less favourable, they added.

Peltz and Taneja said Janus Henderson had an opportunity to grow but was best placed to do so "free from the constraints of operating as a public company".

General Catalyst is a Silicon Valley-based venture capital group with a focus on transforming industries with applied AI and raised $8bn last October.

The offer comes as flows at Janus Henderson, which has assets of $457bn, have improved in recent quarters. It has formed new partnerships and attracted money into its actively managed exchange traded funds.

The US group has struggled to compete after the merger of Denver-based Janus Capital and London-based Henderson Group left it racked by internal dissent and low-cost passive fund managers took market share.

Trian first disclosed an investment in Janus Henderson in October 2020, when its share price was about half the level it is now. Peltz was appointed to the board at Janus Henderson in 2022, helping to install its chief executive Ali Dibadj later that year.

Janus Henderson said its board would appoint a special committee to consider the proposal, which was submitted on October 26. There was "no assurance" that a deal would result, it added.

Peltz has a record of targeting mid-tier asset managers. As an investor in Legg Mason, Trian helped steer the US investment house towards a deal with rival Franklin Templeton in 2020 -- a transaction that created a $1.5tn fund giant.

Nelson Peltz and General Catalyst lodge $7bn takeover bid for Janus Henderson