Cardinal Keith O’Brien argued the presence of Miss Boyle, runner-up of Britain’s Got Talent, and Michelle McManus, 2003 Pop Idol winner, will help the Pope’s message resonate beyond those who are Roman Catholic.
He also argued the £1 million cost to the taxpayer of the Pope’s visit will be far outweighed by the “moral benefits” and welcomed plans by the Rev Ian Paisley to stage a protest in Edinburgh.
Asked about the presence of Miss Boyle and Miss McManus, the cardinal said: “If you've got a good message, and I think we have, there's no harm in marketing it in the very best possible way.
“We want to get as many people as possible to listen to the Pope's message, not just specifically members of our Roman Catholic Church.”
He said it was important to keep the thousands of visitors happy, adding: “You have to do something with them. You can't just have them singing ancient hymns and that sort of thing.”
Benedict XVI's visit on Thursday starts in Edinburgh, where he will be greeted by the Queen and the Duke of Edinburgh at the Palace of Holyroodhouse.
Alex Salmond, the First Minister, will also be there to greet him alongside Nick Clegg, deputy Prime Minister, and leaders of the Welsh and Northern Irish Assemblies.
At the same time thousands of people are expected to take part in the inaugural St Ninian's Day Parade on Princes Street to mark the feast day of Scotland's first saint.
The Pope will travel to Glasgow to celebrate the early evening mass at Bellahouston Park, where 85,000 worshippers are expected to gather.
Cardinal O’Brien said Benedict XVI will find a more secular country since the visit of Pope John Paul II in 1982.
“There is even more need to have someone to proclaim the Christian message to those who want to hear it, and for those who don't want to hear it, fine,” he said.
Rev Paisley, the former Northern Irish First Minister, now Lord Bannside, is leading a delegation from the Free Presbyterian Church to Edinburgh to protest.
The cardinal said he was also from Northern Ireland, adding: “If Ian Paisley didn't come, I wouldn't have thought the visit was worthwhile. It just shows how important this visit is that Ian Paisley's coming along to protest.”
Rev Paisley said he spurred to act by Catholic priests’ abuse of children. The cardinal said he did not know whether the Pope would raise the issue, but he would be “perfectly happy” if it was addressed.
A spokesman for the Catholic Church said the cost to taxpayers will be up to £1 million, but the Scottish economy will benefit by up to £13 million from the visit.
“The moral value far outweighs any cost value. It improves morality in the Catholic Christian community,” the cardinal said.
“It will outweigh any fears, any worries, any depression that folk might feel about the cost. I look forward to it very, very positively.”