Martin signed for a bonus of just over $7 million, well above the No. 5 selection's slot value of $6,180,700, Jim Callis of MLB.com reports.
It's the largest signing bonus in Blue Jays history, surpassing that of 2019 first-rounder Alex Manoah by over $2 million, according to Shi Davidi of Sportsnet.
Martin's deal is also the second-highest bonus given to this year's draftees behind only first overall pick Spencer Torkelson, and the 12th-largest in MLB history, according to Callis.
The Vanderbilt star fell to the Blue Jays at No. 5 overall despite many evaluators ranking him as the best all-around player in this year's draft. He played six different positions during his freshman season at Vanderbilt before settling in at third base. The 21-year-old was announced by the Blue Jays as a shortstop.
Martin is represented by agent Scott Boras, who also negotiated left-hander Hyun-Jin Ryu's four-year, $80-million deal with Toronto this past winter.
The Blue Jays also announced the signing of fourth-round pick Nick Frasso, a right-hander from Loyola Marymount. Frasso received a $459,000 bonus, according to Jonathan Mayo of MLB.com.
Toronto has signed all five of its 2020 draft picks. The Blue Jays spent exactly 5% over their 2020 bonus pool allotment, the highest allowable amount without being stripped of future draft picks, according to Callis.