Odey (pictured) bought 22.5 million shares in Circassia – a stake worth almost £70 million and equivalent to 12% of the business.
According to a filing on the London Stock Exchange, the holding is spread across a number of funds, with Crispin's Odey European fund holding 3.79% and all other funds holding less than 3%.
The flotation of Oxford-based Circassia was the biggest in the UK’s biotech sector for decades, and at an initial launch price of £3.10 valued the firm at the very top of the expected range.
Circassia specialises in the development of allergy therapies, and it plans to use the proceeds from the listing to roll out its cat allergy treatment and develop other products for grass and dust-mite allergies.
It lost £20 million in 2013, but is now valued at almost £600 million.
'This is a milestone achievement in Circassia's history which demonstrates the significant progress we have delivered over the past seven years,' Circassia chief executive Steven Harris told the stockmarket last week.
He added: 'We have been met with an enthusiastic response from investors across the UK, US and EU who have recognised the significant potential of our product portfolio and platform technology.
'As a result, we now have funds to bring Cat-SPIRE to market; the first of a new generation of allergy immunotherapy products that have the potential to overcome the limitations of current treatments.'
Odey’s firm, which he launched in 1991, oversees more than £7 billion of assets.
Crispin Odey personally runs a range of funds, including the Odey Pan European fund and is + rated by Citywire.
According to Citywire data, the fund has returned 32.8% over the past three years, compared with an average of 25.8% from his peer group.
He is also a renowned shorter of stocks, and among others is currently betting against Manchester United and Sainsbury’s.