He attended private workouts and visits with a few teams, including the Dallas Cowboys, Tennessee Titans, New York Jets, Buffalo Bills, and New Orleans Saints.

Head coach Sean Payton named Vaccaro the backup strong safety behind Harper to start the regular season.

On September 22, 2013, Vaccaro recorded seven combined tackles, broke up a pass, and made his first career interception during a 31–7 win against the Arizona Cardinals in Week 3.

[17] In Week 5, he collected five solo tackles, deflected a pass, and made his first career sack on Jay Cutler in the Saints' 26–18 win against the Chicago Bears.

[19] On December 22, 2013, Vaccaro was carted off the field during the first quarter of the Saints' 17–13 loss against the Carolina Panthers after breaking his ankle while making a tackle.

[21][22][23] Vaccaro finished his rookie season with 79 combined tackles (62 solo), eight pass deflections, a sack, a forced fumble, and an interception in 14 games and 14 starts.

[25] Vaccaro entered training camp slated as the starting strong safety after Roman Harper departed for the Carolina Panthers during free agency.

[33] Vaccaro started in all 16 games in 2015 and recorded a career-high 104 combined tackles (71 solo), five pass deflections, three sacks, and a forced fumble.

[30] On April 12, 2016, the Saints exercised the fifth-year option on Vaccaro's rookie contract and agreed to pay him $5.76 million for the 2017 season.

On November 10, 2016, it was reported that Vaccaro was facing a four-game suspension for violating the league's policy on performance-enhancing drugs for using Adderall and planned to appeal.

[37] He finished the season with 68 combined tackles (51 solo), five pass deflections, two forced fumbles, an interception, and a sack in 11 games and 11 starts.

[30] Vaccaro entered training camp facing competition from Vonn Bell and rookie second-rounder Marcus Williams.

[38] On October 15, 2017, Vaccaro recorded four combined tackles, a season-high three pass deflections, an interception, and scored a touchdown during a 52–38 victory against the Detroit Lions.

During the first quarter, Vaccaro recovered a fumble in the end zone after Alex Okafor stripped it from quarterback Matthew Stafford.

[42] Vaccaro finished the season with 60 combined tackles (48 solo), seven pass deflections, 3.5 sacks, a fumble recovery, and a touchdown in 14 games and 14 starts.

[43] On August 4, 2018, Vaccaro signed a one-year, $1.5 million contract with the Tennessee Titans after starting strong safety Johnathan Cyprien suffered a season-ending torn ACL.

[49] In the Divisional Round of the playoffs against the Baltimore Ravens, Vaccaro intercepted a pass thrown by Lamar Jackson during the 28–12 road victory.

[50] In Week 2 against the Jacksonville Jaguars, Vaccaro led the team with 11 tackles and made his first sack of the season on Gardner Minshew during the 33–30 win.

[55] Vaccaro traveled to Kenya during the 2016 offseason with former Texas and Saints teammate Alex Okafor and is involved in community and fundraising efforts to construct a school in the region.

[57] On April 19, 2024 YouTuber and Twitch streamer GernaderJake announced on X that he is suing G1 over an unpaid $100,000 loan that he claims "Kenny is personally liable for.