Greene King will continue to supply its own beer brands to the pubs for the next three years under the deal, expected to wrap up within a month.
Hawthorn Leisure, backed by Avenue Capital Group and May Capital, is led by former Enterprise Inns managing director Gerry Carroll.
The 275 pubs due for sale delivered earnings of £12.4m for Greene King last year.
Greene King now expects to reduce its estate to just 750 tenanted and leased sites – significantly fewer than the 1,200 sites it planned in 2010.
Chief executive Rooney Anand said: “We believe that a smaller estate than originally envisaged is now more appropriate going forward as we move increasingly to higher growth areas in our markets and to improve the customer offer.”
On Wednesday, Greene King said it would meet full-year forecasts after strong sales growth had continued in its fourth quarter.
Shares in the firm closed down 1.7 per cent at 875p yesterday.