Both charities will operate side by side under the Ypeople Group brand, a spokesman for the organisations said, with the aim of expanding and strengthening the support the charities offer throughout Scotland.
Ypeople, which was formed in 1824 as the Glasgow Young Men’s Society for Religious Purposes and latterly became YMCA Glasgow, provides support to vulnerable men and women and employs almost 200 people.
YWCA Scotland, which has seven staff, is a feminist organisation supporting young women and girls. It had an income of £212,000 in the year to the end of March last year. Ypeople had an income of £5.6m during the same period.
A spokesman for the organisations said there would be no redundancies or job losses as a result of the merger, which was officially launched yesterday.
YWCA Scotland will maintain its offices in Edinburgh and a centre in Glasgow that provides services to local women. Ypeople will continue to maintain the 20 services it runs across Scotland.
Joe Connolly will continue as chief executive of Ypeople and Patrycja Kupiec will retain her role as director of YWCA Scotland.
The charities will maintain two trustee boards, with one place on each for a representative from the other organisation.
Connolly said the two organisations already had much in common. "The two groups have rich histories dating back more than 100 years but, at the same time, take a modern and outward-looking approach to supporting and giving a voice to vulnerable and marginalised people across Scotland," he said.
Kupiec said: "The partnership with Ypeople will strengthen our position as one of Scotland’s leading feminist organisations and we are very excited about this next step in our history."