Normally one of the hottest tourist tickets in town, the home of Michelangelo's celebrated ceiling frescoes was to close its doors early to regular visitors to enable the group of around 150 street-sleepers to be shown around the chapel and adjoining Vatican museums and gardens.
It was the latest in a string of highly symbolic initiatives sanctioned by Francis, who has made a focus on the plight of the homeless and other marginalized groups one of the defining themes of his papacy.
Last month a homeless man who died on the streets around St Peter's was buried in an exclusive cemetery within the Vatican that is usually reserved for senior German clerics.
The Argentinian Pope, who says he wants "a poor church, for the poor," has had showers for the homeless installed in public toilets just off St Peter's square.
To mark his 78th birthday in December, he ordered the distribution of sleeping bags across Rome and some homeless people have been recruited to hand out copies of the gospels to the faithful attending Sunday audiences at St Peter's.