In his address, Francis stressed that the job of cardinal was "not an honorary title" and that it involved working at the centre of the church in a manner that "must be exercised in charity, and is ordered towards charity."
“Those called to the service of governance in the Church need to have a strong sense of justice, so that any form of injustice becomes unacceptable, even those which might bring gain to himself or to the Church," Francis told the new cardinals.
Archbishops from Myanmar, Thailand, Uruguay and Cape Verde were among the senior members of the Catholic Church who were appointed cardinals on St Valentine's Day.
The 15 elector cardinals come from 14 countries. The five other cardinals are above the age of 80 and therefore already ineligible to take part in the conclave that will elect the next pope.
Germany's Karl-Josef Rauber was among the group of over 80-year-olds.
Among those taking part in the ceremony in St Peter's Basilica was retired pope and fellow German Benedict XVI, who was greeted warmly by Francis.