Rupert and Jo Clevely are expected to pocket around £8m in cash as part of the deal.
Rupert Clevely will also join the Young’s board.
Geronimo manages 22 pubs in central London, three at Heathrow and one in Surrey, with a strong focus on food.
Young’s plans to keep running Geronimo as a separate division – but said the acquisition was an “excellent fit” with its long term expansion plan.
Young’s chief executive Stephen Goodyear said: “In addition to its ethos, existing estate and attractive pipeline of new pub opportunities, Geronimo brings expertise in operating both leases and concessions at high footfall locations, with pubs at Heathrow airport, St Pancras International train station and the Westfield London shopping centre in Shepherd’s Bush.”
The Clevelys opened their first pub, the Chelsea Ram in south west London, in 1995 after returning from Australia.
They were influenced by the “warm and cosy” pubs they had seen in Sydney.
Rupert Clevely said: “Key to our success is the entrepreneurial flair and individuality, proven food expertise and home-from-home hospitality for which Geronimo is renowned.”
Penta Capital, the Scottish private equity firm held a 49 per cent stake in Geronimo Inns. The Clevelys own 33 per cent of Geronimo, which made a profit of £6.1m last year.
It is expected to post earnings of just over £8m in 2011.