Shares in Jupiter rose on news of the management revamp, which follows a turbulent period for the British fund manager.
Its shares fell more than 50 percent in 2018 as volatile markets prompted skittish investors to withdraw billions of pounds in assets.
In a statement on Tuesday, Jupiter said its board had identified Formica as a potential successor to Slendebroek as part of its long-running corporate leadership planning.
In light of his current availability, the board decided to accelerate plans to appoint Australian-born Formica, with Slendebroek's support.
"Mr Formica is well known by the market and investors, hence this news should be taken positively by the market," KBW analyst Jonathan Richards said in a note to clients, flagging a 'market perform' rating and 480 pence a share target price.
"His appointment and subsequently realignment of the business could be the catalyst that Jupiter shares need to re-rate over 2019."
Jupiter shares were up 1.4 percent at 331.3 pence by 0934 GMT, outperforming a flat FTSE mid-cap index <.FTMC>, and have regained 11 percent since the start of 2019 as markets bounced.
Formica is known for an acquisitive, hands-on management approach and speculation about Jupiter's fate as an independent, publicly listed company is likely to continue under his watch, industry sources said.
Slendebroek has agreed to remain at the company until May 1 to ensure a smooth leadership transition and handover.
While Jupiter has seen heavy outflows, 77 percent of its funds did outperform median returns in the year to end-2018.
Formica is expected to continue with Slendebroek's active, globally-minded growth strategy. Jupiter has attracted 5.5 billion pounds ($7 billion) of new money from non-UK investors in the last six years, while Slendebroek was head of the firm's distribution and strategy from 2012 to 2014, and in the last four years when he was CEO.
Formica was previously chief executive of Henderson Group and later co-chief executive of Janus Henderson Group after its merger with Janus Capital in 2017, but left the firm last year.
"He was seen as a strong leader at Henderson and many of the investors we spoke with were surprised by his departure," UBS analyst Michael Werner said in a note to clients, but added he had "his work cut out to grow Jupiter's institutional business".
"We think it will take some time for investors to return to Jupiter's fund platform given the struggles it faced in 2018. We retain our 'Sell' rating despite the positive reaction we expect on today's news."
($1 = 0.7772 pounds)
(Reporting By Sinead Cruise, editing by Rachel Armstrong/Lawrence White/Susan Fenton)
By Sinead Cruise and Simon Jessop