Beal, who was taken with the second pick in the third round Wednesday, is the highest-drafted player in the supplemental draft since wide receiver Josh Gordon went in the second round in 2012.
The only other player taken in year's supplemental draft was Virginia Tech cornerback Adonis Alexander, who was selected by the Washington Redskins in the sixth round.
"We feel like we're getting our third-round pick now," general manager Dave Gettleman said in a statement. "We discussed it at length yesterday, and had a great conversation. We basically had a draft meeting in the office, with people on the speaker phone who had seen him. It was a very thorough conversation."
Gettleman added: "We're very, very excited about getting Sam in the draft."
Beal, 21, declared for the draft this spring because his academic eligibility was up in the air. The promising cornerback, who was a two-year starter at Western Michigan, provides the Giants with an injection of talent at a position of need.
It was evident this spring that the Giants were extremely thin behind starters Janoris Jenkins and Eli Apple. The Giants had William Gay, 33, playing with the first-team defense in the slot this spring and had a bevy of career journeymen fighting for spots in their secondary.
Beal, who is known as a cover corner, immediately joins that crowded group and should be able to compete for a role this season.
The Giants were one of 32 teams that reportedly were in attendance for Beal's pro day, where he impressed scouts with his athleticism and size. The 6-foot-1 cornerback ran the 40-yard dash in the 4.5 range and had a 37-inch vertical leap.
The question on Beal is his strength, according to one scout familiar with the prospect. He weighed 178 pounds at his pro day and his tackling was questionable on tape.
It was Beal's ability to lock down receivers that made him the first supplemental pick since the Rams selected offensive lineman Isaiah Battle in the fifth round of the 2015 draft.
Beal started 11 games as a junior in 2017 and was named second-team All-MAC. He had two interceptions, one forced fumble, 26 tackles (including three for a loss) and 10 pass breakups. His first career interception came against Sam Darnold and USC in the season opener.
Beal had eight pass breakups in his first year as a starter in 2016.
There had been 45 picks in the history of the supplemental draft, according to Elias Sports Bureau. Of those 45 players, eight have gone on to make the Pro Bowl during their NFL careers.
Wide receiver Cris Carter is the only Pro Football Hall of Fame player to come from the supplemental draft.
Having lost their third-round pick in the 2019 NFL draft, the Giants now have six selections with the potential for seven if they recoup a conditional seventh-round pick used to acquire punter Riley Dixon from the Denver Broncos earlier this year.
The Giants had previously taken two players in the supplemental draft -- cornerback Tito Wooten (fourth round) in 1994 and quarterback Dave Brown (first round) in 1992.