Connect Assist will take on 12 staff to run the Â£2m Veterans' Gateway at Nantgarw, near Cardiff.
Advice on housing, finance and health will be on offer, pointing veterans to the relevant charities and support.
Veterans Minister Tobias Ellwood said it drew together "all facets of support" for veterans and families.
Connect Assist already runs a helpline for the Royal British Legion, which led the consortium launching the new service.
The Ministry of Defence, armed forces charity SSAFA, Combat Stress and Poppyscotland are also involved.
Veterans are among the people being hired to offer support to those contacting the service.
"The vast majority of our people make a smooth transition from military to civilian life," Mr Ellwood said.
"But the Veterans' Gateway provides extra support in the form of a staffed, 24-hour, one-stop-shop offering guidance on housing and employment, finance, mental and physical health.
"Our Â£2 million investment honours the nation's Armed Forces Covenant and draws all facets of support for our Armed Forces community together for the first time."
The service has been set up in response to Lord Ashcroft's 2014 Veterans' Transition Review, which reported people's confusion about who they should turn to for help.
Charles Byrne, director general of the Royal British Legion, said: "Veterans' Gateway will make it easier for them to get the support they need, from whoever is best able to provide it.
"No matter how complex their needs, working together we can do more."
South Wales has been chosen as the base for a new 24-hour helpline for armed forces veterans from across the UK returning to civilian life.