Rubio's cousins, who granted an interview to BuzzFeed, told the website that their mother convinced her sister — Rubio's mother — to join the church when they moved to Nevada. Rubio was described as an enthusiastic member of the Mormon Church who was fascinated with the Osmond family and Mormon culture in Utah:

Right when they moved here, they started going to the church activities with me," said Michelle, who grew close to Rubio and his sister, Veronica. "Our parents didn’t let us hang out with non-family members too much. They were pretty strict."
It wasn't long before the Rubios were sitting down with Mormon missionaries, reading the Book of Mormon and preparing for baptism. It's unclear how many in the family ultimately converted; the Denises recalled only the baptisms of Marco, Veronica, and their mother, Oria. But one family member definitely abstained: Marco's father, Mario.
An overworked bartender at Sam's Town Hotel and Casino, Mario had little use for a religion that promoted a strict code of moral conduct that seemed at odds with the way he made a living, said Michelle.
As the family patriarch toiled to support his wife and children, Michelle said Marco — or "Tony" as the family calls him, after his middle name Antonio — stepped in at a very young age as a natural leader in the family. Smart, confident, and slightly stubborn, Rubio was skilled at persuading his siblings, cousins and even his mother to see things his way, Michelle said.
"I think we always thought he'd be something because he had a big mouth, and he was very bossy," she said. "He could convince his mom to do anything."
And for a number of years during his early adolescence, that meant enthusiastically encouraging participation in his family's new church.
"He was totally into it," Michelle recalled. "He's always been into religion. Football and religion. Those were his things."

Over the years, he and his cousins frequented LDS youth groups, attended church most Sundays — often walking to the chapel because his mother didn't know how to drive — and latched on to the mainstream Mormon culture that was easily accessible in LDS-heavy Nevada.

Rubio ultimately converted back to Catholicism, and received his first communion in 1984, at age 13. His family describes him as the motivating force behind the conversion and being among the family's most active participants in religious life.

It's unclear what effect — if any — the news will have on Rubio's political future. A recent poll by Fairleigh Dickinson University indicates that Rubio was the top choice of GOP loyalists for the party's vice presidential nomination, edging out New Jersey Gov. Chris Christie. But with Mitt Romney — a practicing Mormon — the presumptive favorite for the GOP nomination, Rubio's selection might concern some seeking more religious diversity on the ticket.

Some Republicans, in particular Deep South evangelicals, have traditionally had a complicated relationship with the faith. A Pew Survey of white, evangelical Protestants released in November found the group less likely to consider Mormonism a Christian faith, less likely to associate the religion with positive terms, and less likely to support Romney. But the same group was overwhelmingly willing to back Romney in a general-election showdown against President Obama, underscoring that a Mormon faith was unlikely to be a dealbreaker for core Republican voters.

This article was updated at 11:30 p.m. to correct the age at which Rubio converted to Catholicism.