Pope John Paul II and Pope John XXIII will be declared saints on 27 April 2014.
Pope Francis announced in July that he would canonise the two, after approving a second miracle attributed to John Paul.
Polish John Paul, the first non-Italian pope for more than 400 years, led the Catholic Church from 1978-2005.
Pope John was pontiff from 1958-1963, calling the Second Vatican Council that transformed the Church.
Correspondents say the decision to canonise the two at the same time appears designed to unify Catholics.
John Paul II is a favourite of conservatives, while John XXIII is widely admired by the progressives.
The BBC reports the double canonisation will be the first in the Church's history and two popes will attend: Pope Francis and his predecessor Pope Benedict XVI who retired earlier this year.