The acquisition includes the 26 Geronimo pubs, based in central London, Heathrow and Surrey.
It increases Young's managed estate by more than a quarter to 148 pubs, and takes its total estate to 247 pubs.
Young's said it expected the transaction to fuel higher earnings in the first full year of ownership.
The management team of Geronimo will be staying with Young's.
Rupert Clevely, chief executive of Geronimo, will join the Young's board with immediate effect as managing director.
He said: "Young's is the perfect home for Geronimo and I am delighted that the Young's board wants to continue to embrace and retain Geronimo's inimitable DNA."