It's the first time the Steelers have chosen a cornerback in the first round since 1997 when they drafted Chad Scott out of Maryland.
The Steelers would have been happy with either William Jackson III or Burns. Jackson, from the University of Houston, was taken by the Cincinnati Bengals one spot earlier with the No. 24 pick.
Burns, who is 6-feet and 197 pounds, entered the NFL Draft after his junior season. He recorded six interceptions last season and developed into one of the top cornerback prospects in the draft despite dealing with the death of his mother in the middle of last season.
"We're extremely happy to have this one," Steelers general manager Kevin Colbert said. "There is a premium on big corners in this league. When you find someone with that kind of length, speed and athleticism, and couple that with six interceptions, that was very impressive. He's only played three years and only started two so there's tons of upside to him. I know coach (Mike Tomlin) is excited. He likes to get those young guys."
Burns, who turns 21 Sunday, continues a trend for the Steelers, who have selected younger players in the first and second rounds in recent years. Linebacker Ryan Shazier and defensive lineman Stephon Tuitt, the top two picks in the 2014 draft, also came out as underclassmen.
Colbert admitted Burns must develop his skills to become a well-rounded player, but Tomlin is intrigued about his potential.
"We're excited about the upside," Tomlin said. "He's a natural bump corner. He's good with the ball down the field. He has elite speed. He was also a track man down at Miami."
The Steelers had to upgrade their secondary after finishing last season 30th in the league against the pass. They also let starting cornerback Antwon Blake and nickel back Brandon Boykin walk in free agency.
Colbert said the first round of the draft broke well for the Steelers. He said it was an easy selection to make.
"It was real easy," Colbert said. "It was breaking pretty tight. We felt we had a good chance to get a corner. There was quality from top to bottom. We're fortunate he made it to us.
"We started to see this draft class come together this November. We started to get a feel this would be a strong corner class. It really turned out to be just that. We were really fortunate. We're excited to have him."
Burns is taking care of two younger siblings after his mother died, and he has a 19-month old son.
"It was a roller coaster," Burns said of the past year. "With my mom passing, that was unexpected. That motivated me to keep on going."
Burns' first and last interceptions as a college player came at Heinz Field, which shares a home field with Pitt.
In rounds 2 and 3 Friday, the Steelers could turn their attention to a safety. Will Allen, their starter last season, is a free agent and has not been re-signed.