Peter Phillips, the queen’s eldest grandson, may have to give up his place in the line of succession to the throne after it emerged that his bride-to-be is a Roman Catholic.

The engagement between the 29-year-old son of the Princess Royal and Autumn Kelly, a Canadian management consultant, was announced by Buckingham Palace last week. But no mention was made that Ms. Kelly, 31, had been baptized as a Catholic, a fact that could prove embarrassing to the royal family and the government. The 1701 Act of Settlement bars monarchs and their heirs from becoming or marrying Catholics, a source of anger for church leaders who have repeatedly called for its repeal. Under the act, Mr. Phillips will be required to renounce his right to the throne — he is 10th in line at present — or Ms. Kelly will have to formally give up her membership of the church.

Buckingham Palace said yesterday that a wedding date had not been set and “if a decision has to be made, it will be made at the time of the marriage.” Little is known about Ms. Kelly, who moved to Britain shortly after meeting Mr. Phillips at the Canadian Grand Prix in Montreal in 2003.

The Tablet, the Catholic weekly, has now established that she was baptized on June 18, 1978, at St. John Fisher parish church in Point-Claire, a suburb of Montreal. A spokesman for the church told the Daily Telegraph that Ms. Kelly’s mother, Kitty, had authorized the information to be disclosed, saying that her daughter was proud of her religion.

John Gummer, the former Tory minister who is a convert to Catholicism, said: “It is inhuman in the 21st century for anyone to demand this.”

Mr. Phillips, like his sister Zara, has no royal title.