Next month's Super Bowl broadcast, which garners an enormous TV audience, will feature an advert paid for by an anti-abortion evangelical Christian group.

A former college football star known for his outspoken beliefs will appear in the costly 30-second spot bought by Focus on the Family, a Colorado-based ministry influential in Christian conservative politics.

Nearly 100 million Americans are expected to tune in to Super Bowl XLIV on 7 February in Miami Gardens, south Florida. The adverts attract nearly as much attention as the game itself, with Americans watching to see how brands vie for consumers' attention. The Focus on the Family advert is a rare spot from an advocacy group.

The advertisement will feature Tim Tebow, former champion quarterback for the University of Florida football team, who painted Bible quotations under his eyes during games. Focus on the Family and CBS television, the network broadcasting the game, did not disclose the cost of the advert, but media analysts say the cost of a 30-second spot will run between $2.5m and $2.8m.

The advert, entitled Celebrate Family, Celebrate Life, will feature Tebow and his mother Pam, who will tell what the group describes as an inspiring story from her life. It has not released details of the advert, but US media have speculated that she will describe a 1987 pregnancy during which she became ill on a missionary trip to the Philippines. She ignored medical advice to have an abortion, instead giving birth to Tim.

"We're not trying to sell the American people a car or a soft drink," said spokesman Gary Schneeberger. "We're celebrating families."

Schneeberger said the group hopes to influence couples having "struggles" in their marriage. Tebow's father, Bob, runs a group that leads evangelical missions in the Philippines and founded an orphanage there.

The Super Bowl airs alongside creative but often crass adverts for beer, car manufacturers and internet companies, and the network that broadcasts the game normally shies away from controversy. In addition, advocacy groups typically lack the budget to purchase Super Bowl airtime. Focus on the Family said the funds were provided by wealthy supporters.

"They've vetted us," Schneeberger said of CBS. "They know who we are."

Previous advocacy adverts during the Super Bowl have included anti-drug and anti-tobacco spots.

Jon Swallen, senior vice-president of research at media tracker TNS Media Intelligence, said the ad had fuelled media speculation and encouraged buzz in order to maximise publicity.

Between 95 and 100 million people tuned in last year to watch the Pittsburgh Steelers defeat the Arizona Cardinals in Super Bowl XLIII. The game generated $213m in advertising revenue.