The former guard told weekly newspaper Schweiz am Sonntag that he received up to 20 “unambiguous requests” from members of the clergy, including a dignitary close to Pope John Paul II.
His experience in the 110-man security force, he said, gave credence to reports that a “gay lobby” is active in the Vatican.
The former guard recalled being called in the middle of the night by a senior official who invited him into his room.
In another case, he found a bottle of whisky in his room with a visiting card left by a bishop.
A priest, he said, invited him to dinner, saying that the guard would serve afterwards as dessert.
He also claimed that a high official fondled him.
The ex-guard said that he reported the cases to his superiors, complaining of harassment, but received no support for his allegations.
Urs Breitenmoser, a spokesman for the Swiss Guard, told Schweiz am Sonntag that “the rumour of a homosexual network in the heart of the Vatican was not a problem”.
Moser said the preoccupations of the guards were “above all religious and military”.
But the ex-guard said his experience had shaken his belief in the church.
He said he could not understand the “hypocrisy” of those who oppose sex outside of marriage and support the excommunication of divorcees.
In November, current Pope Francis said at a news conference that he wouldn’t judge priests for their sexual orientation.
“If someone is gay and he searches for the Lord and has good will, who am I to judge?” the pope said.
“We shouldn’t marginalize people for this,” he added.
“They must be integrated into society.”
Francis said that gay priests should be forgiven and their sins forgotten in a shift from his predecessor Pope Benedict XVI who ruled that gays should not be priests.
The Swiss Guard was shaken earlier by a gay controversy at the Vatican in 1998 when its commander Alois Estermann and his wife were shot dead by young guard Cédric Tornay, who later turned the gun on himself.
According to a book about the Vatican by British journalist John Follain, Tornay and Estermann had a homosexual affair.
Estermann subsequently had a relationship with another guard and refused to award a three-year service medal to Tornay, which led the guard to kill him, Follain maintains.
Last July, an Italian weekly reported that Battista Ricca, appointed by Pope Francis to a top position at the Vatican bank, had had sexual relations with a Swiss army officer, amongst others.
A Vatican spokesman dismissed the report as “not credible”.