According to media reports in November of the previous off-season, Martin was to captain one of four franchise-style AFLX teams in an upcoming pre-season tournament in 2019. Martin was replaced in the reported line-up by teammate Jack Riewoldt after seemingly removing himself from availability before the tournament concept was confirmed. Instead, he made his first footballing appearance of 2019 in each of Richmond's two pre-season matches in early March. In round 1 Martin was described by AFL Media as "solid, yet not spectacular" with 30 disposals and seven inside 50s in his club's 33-point victory over Carlton. The following week he was tagged effectively by Collingwood's Levi Greenwood and held to just 19 disposals in Richmond's round 2 loss to Collingwood. The strategy was repeated by the Giants in round 3, when Matt de Boer managed to restrict him to just 15 disposals. Martin was undisciplined in response, attracting an AFL fine and significant media scrutiny for an obscene gesture towards Giants ruck Shane Mumford and facing a Match Review report for an off-the-ball hit on defender Adam Kennedy. Initially Martin was offered a two-week suspension for the incident which the AFL's Match Review Officer classed as intentional conduct and high contact with medium impact to the head. Martin challenged the classification at the AFL Tribunal where the impact was downgraded, with the suspension subsequently reduced to one match. He was among Richmond's best players upon his return in round 5, kicking three goals and gathering 25 disposals after a tagging effort by Sydney's George Hewett saw him play long stints as forward. Martin was again subject to tagging in round 6, this time kept to 17 disposals and a single goal by Melbourne's Michael Hibberd. In round 9 Martin was spectacular, turning in a performance labelled my multiple media outlets as evocative of his best from his 2017 Brownlow-winning season. He recorded 13 disposals and four clearances in the first quarter of the win, before finishing the match with 37 disposals, 10 clearances and two goals. He earned 10 Coaches Award votes that match and was named in AFL Media's Team of the Week, a feat he repeated after 25 disposals and eight clearances in round 10. For the second time that season, Martin kicked three goals in round 11's loss to North Melbourne. In round 13, injuries to captain Trent Cotchin, vice-captains Jack Riewoldt and Alex Rance as well as to early-seasons stand-in captain Shane Edwards saw Martin called upon to captain Richmond for the first time in his career. He performed well with 32 disposals, nine marks and two goals, earning a club-best three coaches votes despite an eventual loss to Adelaide in that match, the last before the club's mid-season bye. At that point he held averages of 25.3 disposals and 1.1 goals per game and was labelled by AFL Media as a mid-season contender for a fourth-straight All-Australian selection. Martin was exceptional again following the bye, earning three Brownlow votes and the Ian Stewart Medal for best-on-ground with a game-high 36 disposals and six clearances against St Kilda in round 15. Martin was named to AFL Media's Team of the Week in rounds 18 and 19 after recording a personal season-high 38 disposals in the latter of those two matches. His seven coaches award votes also saw him move into 18th place on the award's leaderboard. He bested that mark with nine votes as best afield with 34 disposals and 11 inside-50s in round 20's win over Melbourne, again earning Team of the Week honours. Martin suffered general soreness and was a late withdrawal from the following week's match, before returning with what multiple media outlets labelled one of the best performances of his career in round 22's win over West Coast. In addition to a game-high 35 disposals and 818 metres gained, Martin set a new career-best with 13 inside 50s, which was also the most by any player in the league in a match that season. At the end of the regular season Martin was named in the squad of 40 players for the All-Australian team but missed out on selection to the final 22. Martin was however named to the best 22 in The Age chief football reporter Jake Niall's and the Herald Sun chief football reporter Mark Robinson's teams of the year along with selection in the AFL's Player Ratings team of the year and also placed equal-11th overall in the coaches association player of the year award. Martin's 23 Brownlow Medal votes saw him finish with the equal-sixth most votes (though officially ineligible due to suspension) and saw him pass Kevin Bartlett for the record for most votes by a Richmond player in club history. In Richmond's first final Martin was a stand-out best on ground, kicking a career-high six goals in a 47-point qualifying final victory over the Brisbane Lions. That tally was the most by any Richmond player in a final since Bartlett in the 1980 grand final. In the preliminary final win over Geelong a fortnight later, Martin recorded 22 disposals and two goals, restricted somewhat by a knock to the leg suffered in the match's first quarter. For the second time in three seasons, Martin was a premiership player and again Norm Smith Medalist as best on ground when his Richmond side defeated Greater Western Sydney in the grand final the following week. Martin kicked four goals and recorded 22 disposals to be unanimously selected for the Norm Smith. In doing so he became just the fourth player in AFL/VFL history to win the award twice. Martin also repeated his feat of 2017 in again receiving the Gary Ayres Award as the player of the finals series, and placed sixth in the club's best and fairest count. At the end of the season and finals series, Martin was ranked by Champion Data as the league's fourth best player that year while Herald Sun chief football reporter Mark Robinson ranked Martin number one on his list of the league's best players in 2019.