Candles bearing the pontiff’s likeness were burned by snaking queues of devotees along the passageway to the mausoleum, in the north of the capital Port Louis, where Father Jacques Désire Laval was entombed after his death in 1864.
Vendors sold flowers to pilgrims singing on their journey to the hillside tomb, many from Mauritius' Hindu and Muslim faiths.
Laval, who was sent to the island after the island abolished slavery, is today revered across the religious divide, known popularly as the "Apostle of Mauritius".
The anniversary of his death every September draws huge crowds to St Croix, where he is buried beneath a grand shrine overlooking the capital.
“I think he is the one who unites all Mauritians. I have never heard any Mauritian tell me he did not care about Father Laval,” Father Gérard Guillemot, a priest in Mauritius, told AFP.
“For everyone, Laval is like a father.”
Most of Mauritius is Hindu, but there are sizeable Christian and Muslim minorities, and the tiny island of 1.2 million people is proud of its religious unity.
At Laval’s tomb, a Hindu woman said she made the pilgrimage every year to pray for her ill granddaughter, laying flowers alongside Christians offering their own prayers.
Mauritians of other faiths offered food and refreshments to pilgrims along the winding route up the hill.
“The celebration of Father Laval is important to me because it unites all Mauritians together, small and big, all the different groups who live in Mauritius," said Maria, a devotee who only offered her first name.
Every year, the annual pilgrimage crosses from the evening of September 8 to the early morning of the next day, marking the date of Laval's death.
This year, on the 155th anniversary of his death, the celebrations have been brought forward to accommodate Pope Francis’ tour of Mauritius, the first by a pontiff to the tiny Indian Ocean island since John Paul II in 1989.
Pope Francis will arrive Monday from Madagascar, after having toured Mozambique on a three-nation tour of Africa.
The yellow and white flag of the Vatican has been flying across Mauritius ahead of the pontiff’s visit, and billboards have projected his likeness across the island.
Laval was beatified in 1979 but many devotees hope Francis will advance the case for the French priest’s canonisation into sainthood.
Francis will visit Laval’s shrine, in between political engagements and holding a mass in Port Louis that will be beamed on huge screens across the capital.