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.
"Both Cardiff City Football Club and Cardiff Blues have already agreed a new training headquarters at the Vale of Glamorgan Resort.
"And the announcement today further demonstrates how important it is for major sporting brands in Cardiff to be working together for the benefit of the wider community.
"Today is an important day in Cardiff City's future sporting history."
Blues chief executive Robert Norster added: "We positively look forward to a new beginning for both codes in a stadium and facilities designed for modern-day teams and supporters alike.
"Our shared training ground at the Vale, together with the new stadium, will undoubtedly play a major part in our combined efforts to move our respective teams forward.
"The move will also ensure we can advance and develop further the Cardiff Blues region in the increasingly-competitive world of professional rugby."