Harvard divinity professor Karen King unveiled the 4th-Century Coptic script at a conference in Rome.
She said researchers had identified the words “Jesus said to them, ‘my wife'”, which might refer to Mary Magdalene.
Christian tradition holds that Jesus did not marry – but Ms King said in early years it was subject to debate.
The provocative find could spark debate over celibacy and the role of women within Christianity, she added.
But the announcement sparked scepticism from some theologians.
Jim West, a professor and Baptist pastor in Tennessee, said: “A statement on a papyrus fragment isn’t proof of anything. It’s nothing more than a statement ‘in thin air’, without substantial context.”
Wolf-Peter Funk, a noted Coptic linguist attending the same conference as Ms King, said there were “thousands of scraps of papyrus where you find crazy things,” and many questions remained about the fragment.
‘Worthy disciple’
Ms King said the document, written in ancient Egyptian Coptic, is the first known scripture in which Jesus is reported to cite his wife.
She said the 4th-Century text was a copy of a gospel, probably written in Greek in the 2nd Century.
She said initially she was sceptical about the yellowish brown papyrus, and started from the notion that it was a forgery – but that she quickly decided it was genuine.
Several other experts agreed, she said, but the “final judgment on the fragment depends on further examination by colleagues and further testing, especially of the chemical composition of the ink”.
Ms King said the script was not proof of Jesus’s marital status.
“It is not evidence, for us, historically, that Jesus had a wife,” she said.
“It’s quite clear evidence, in fact, that some Christians, probably in the second half of the 2nd Century, thought that Jesus had a wife.”
Ms King said it revealed the concerns of early Christians with regards to family and marriage matters.
From the very beginning, Christians disagreed about whether it was better not to marry, but it was over a century after Jesus’s death before they began appealing to Jesus’s marital status to support their positions.
“What this shows is that there were early Christians for whom sexual union in marriage could be an imitation of God’s creativity and generativity and it could be spiritually proper and appropriate.”
Bible scholar Ben Witherington III, a professor in Kentucky, said the term “wife” might simply refer to a female domestic assistant and follower.
Private owner
According to Ms King’s research team, the text also quotes Jesus as telling his followers that Mary Magdalene is worthy of being his disciple.
This, in turn, casts new doubt on the long-held belief that Jesus had no female disciples, and raises issues about Mary’s biblical role as a sinner, the researchers said.
Ms King presented the document at a six-day conference held at Rome’s La Sapienza University and at the Augustinianum institute of the Pontifical Lateran University.
The faded papyrus is hardly bigger than a business card and has eight lines on one side, in black ink legible under a magnifying glass.
The private collector, who owns the fragment, has asked to remain anonymous because “he doesn’t want to be hounded by people who want to buy this”, Ms King said.
She said he had contacted Ms King to help translate and analyse it.
Nothing was known about the circumstances of its discovery, but because of the script used she had concluded it must have come from Egypt.