The new stadium will be able to hold up to 30,000 spectators
Cardiff Blues rugby have committed to playing all their home games at Cardiff City's new stadium in the capital for at least 20 years.
The Bluebirds' new home is due to open in 2009 after which they will start a ground share until at least 2029.
The Blues are due to quit their current Arms Park at the same time along with City who are leaving Ninian Park.
The city's two leading sporting clubs signed a licence agreement set at 20 years to officially seal the deal.
The new £46m ground in the Leckwith area of the city will initially seat 25,000 with the option for the capacity to be increased to 30,000 in the future.
The Blues have said rugby will still be played at the old Arms Park home after the move across the capital with Cardiff RFC playing their home games there.
The club's chief executive Robert Norster said: "We positively look forward to a new beginning for both codes in a stadium and facilities designed for modern-day teams and supporters alike.
"The move will also ensure we can advance and develop further the Cardiff Blues region in the increasingly competitive world of professional rugby."
Cardiff City chairman Peter Ridsdale said: "It's a fantastic day for sport in the city whereby two leading brands will be playing top level sport in the new stadium.
"We are very pleased that Cardiff Blues have signed the licence to play all of their home games at the stadium over the next 20 years."
The two clubs have already been given the go-ahead for a new joint training headquarters as part of a sports academy at the Vale of Glamorgan Resort.