The deal, whose value has not yet been disclosed, is expected to be closed later today.
Delmege Forsythe has interests in retail distribution, travel and insurance broking.
Vallibel One, Dhammika Perera's investment holding company, has planned an IPO opening on June 21 to raise 532 million rupees by selling 21 million shares at 25 rupees a share.
It had a private placement early in 2011 also at 25 rupees and raised 4.9 billion rupees.
Among the firm's assets are listed Royal Ceramics, LB Finance and Sampath Bank.
Funds from the IPO and private placement will be used to build a 300-room hotel as the firm expands its leisure business.
The hotel, costing 5.6 billion rupees (50 million US dollars) is to be built in Negombo in Sri Lanka's western coast, north of the capital Colombo, and will be under a new group firm, Greener Waters Ltd.
The hotel is to be completed by early 2014.
Vallibel One also plans investments in the power sector.