Johnston, 18, is the father of Bristol Palin's baby, Palin's family says.
According to the announcement, Bristol, the 17-year-old daughter of Alaska Governor and presumptive Republican Vice Presidential nominee Sarah Palin, is five-months pregnant.
The word sent shockwaves through the political scene.
Palin is scheduled to address the convention Wednesday night.
CBS News correspondent John Blackstone went to Johnston's hometown of Wasilla, Alaska, of which Palin was once mayor, to profile Johnston.
The high school hockey star's decision to join Bristol and her family at the convention was cheered by locals back home.
"More power to him for being there," said one.
"If he steps up and does the right thing and tries to stand by her, then good for him," said another.
"It sounds to me like at least he's sticking by her, and that's a good thing," said yet another.
When the Palins made the surprising announcement of the pregnancy, they said the young couple planned to wed.
Johnston's mother is quoted as saying this is no shotgun wedding -- that the two teens had plans to marry even before they knew Bristol was pregnant.
On his MySpace page, which has now been made private, Johnston reportedly said he's in a relationship, but didn't want to have kids.
His mother is also quoted as saying she was worried about her son handling the spotlight, noting, "It's difficult enough for teenagers to deal with any pregnancy, and having the entire nation watching makes it worse."
The New York Daily News sheds further light on Johnston.
As the News puts it, "On his MySpace page, Johnston proudly declares: 'I'm a f---in' redneck.'
'I live to play hockey. I like to go camping and hang out with the boys, do some fishing,' he says on the site.
He also warns that if anyone messes with him, 'I'll kick ass.'
The Web site, before it was removed, appeared not to have been accessed for a year.
On it, he admits to having a girlfriend.
On the part where it asks about children, he wrote, 'I don't want kids.' "
The News adds, "Mark Okeson, the assistant principal at Wasilla High School, told the Chicago Tribune that Bristol started her junior year last fall, in the town where Sarah Palin grew up.
He said Bristol inexplicably transferred to an Anchorage high school midyear, leaving Levi behind."