The new charity, whose name has yet to be determined, will be formally constituted in May.
The new organisation will initially be based One Parent Families' offices in London and will be headed up by current One Parent Families' chief executive Chris Pond.
The position of Gingerbread's chief executive, Gwen Vaughan, has yet to be discussed, but Gingerbread chair Jolyon Maugham said that between two and four of Gingerbread trustees would sit on the board of the new organisation to ensure it has the expertise to do Gingerbread's work.
Neither charity is ruling out redundancies. "If there are any, it will be a very small number," said Maugham. "Neither organisation should be concerned with issues of winners and losers. What is important is that the new organisation is one that does the very important work that needs to be done with the utmost efficiency."
Pond said: "We will do everything we can to employ as many staff as we can from Gingerbread, but it is premature to talk about numbers."
He added that the merger, which has been under discussion for two years, aimed to maximise both charities' impact at a time when family policy is receiving a lot of political attention.
"Lone parents have shot up the political agenda as major changes are proposed on key issues like work requirements and child support," he said. "Our merger will mean that lone parents have a louder, unified voice. With Gingerbread's unique network of lone parent groups and One Parent Families' policy expertise there is an excellent fit."