Vlastuin started the 2019 season with appearances in each of the club's two pre-season matches, though played only restricted game time in second due to minor soreness. He was fully fit for the club's season opening match against Carlton, where he contributed 14 disposals. The loss of All-Australian defender and teammate Alex Rance to an ACL injury in that match however, would force Vlastuin into a more defensive role that in seasons past, becoming responsible for negating oppositions teams' third forward. In the week following Rance's injury, Fox Footy analyst David King labelled Vlastuin the Richmond player most capable of replacing Rance's prowess as an intercept player. When all three members of Richmond's leadership group were ruled out from playing in round 4, AFL Media named Vlastuin the front runner to captain the side that weekend, though he would eventually be passed over for the role in favour of veteran Shane Edwards. He was however added to the club's de facto leadership group of five, who served in the role during the appointed leaders' playing absence. Two weeks later Vlastuin would show leadership of another kind, named best on ground with a maximum ten coaches award votes for a 28 disposals performance for which he was also named to AFL Media's Team of the Week. In his next match in round 7, Vlastuin would suffer a minor ankle injury during a loss to the Western Bulldogs. Though he would return to the field to play out the match, a mid-week flare up on symptoms would cause Vlastuin to miss the following week's match as a result of the injury. Vlastuin returned to the side in round 9, playing a dual role as defender and midfielder while kicking his first goal of the year and adding 24 disposals. He suffered a knock to the hip in round 12 that saw him in some doubt for round 13's match against Adelaide, but eventually recovered in time to post 24 disposals. Vlastuin recorded more than 20 disposals in three of his next five games following that match, including in round 19 where he received one coaches award vote for a performance that included his then season-best total of eight rebound-50s. He was named among Richmond's best for 24 disposals in round 20, before earning four coaches votes and selection to AFL Media's team of the week in round 21. Vlastuin closed out the home and away season with a nine mark, 13 intercepts best-on-ground performance that earned him nine coaches votes and yet another selection to the AFL Media team of the week in round 23. He finished the home and away season with the third most intercepts of any player that year and placing 14th for marks, while rating as 'elite' for intercepts and intercept marks by the AFL's statistical partner, Champion Data. In the lead up to the finals series, Vlastuin was named to the best 22 in The Age chief football reporter Jake Niall and the Herald Sun chief football reporter Mark Robinson's teams of the year in 2019. Despite that recognition, he was left out of both the final team and even the squad of 40 players for the official All-Australian award and was identified by Fox Footy and the Herald Sun as one of the most notable omissions. In Richmond's qualifying final win over the Brisbane Lions at The Gabba, Vlastuin recorded a career-best 12 rebound-50s in what Fox Footy described as a 'damaging' performance as a ball carrier at half-back. That earned his side a home preliminary final against Geelong, where Vlastuin's defensive efforts helped his side through to a grand final match up against Greater Western Sydney. To that point, Vlastuin ranked fourth in the league for total intercepts that season. In the grand final, Vlastuin was part of a Richmond defence that kept the Giants to 25 points, their lowest score in the club's eight-year history and the lowest score by any team in a VFL/AFL grand final since 1960. He took a match-high 12 marks, was one of only five players to receive coaches award votes (three votes) and was described by AFL Media as "one of the Tigers' best" players on the day. Vlastuin finished the season with a second premiership in three years and placed fourth in the club's best and fairest count, his best finish to date. He was also named at number 41 in Herald Sun chief football reporter Mark Robinson's list of the league's best players in 2019 and was ninth among all defenders on that same list.