"I’m conservative, but I’m not in a bad mood about it," Pence said Monday.
Pence joins an increasingly crowded field of Republican candidates. His announcement by brings the number of formal Republican candidates to eight.
Several who were reluctant to criticize the GOP front-runner, former President Donald Trump, have begun doing so in the last few days, blasting Trump for, among other things, congratulating dictator Kim Jong-un on North Korea getting a seat on a world health group.
"You don't congratulate a thug. I mean, let's keep in mind this thug has threatened America and threatened our allies over and over again," said former South Carolina Gov. Nikki Haley, candidate for president.
Haley, a candidate for president, attended a weekend event in Iowa, still the first state to vote for Republican presidential candidates early next year, though not for Democratic candidates.
While Pence became the eighth Republican in the running, at least two more are expected to announce this week.
Florida Gov. Ron DeSantis, who's been the target of withering ridicule from Trump, fired back over Trump's happy wishes to Kim Jong-un.
"I was surprised to see that! I mean, I think, one, Kim Jong-un is a murderous dictator. They just imprisoned for life a family, including an infant, which is just outrageous," DeSantis said.
Pence, a former governor of Indiana, is expected to launch his campaign in Des Moines on Wednesday, his 64th birthday.