- Bats Right, Throws Right
- Height 6' 3", Weight 235 lb.
Montero was signed by the St. Louis Cardinals in late 2014. In 2015, he hit .252/.328/.339 for the DSL Cardinals and fielded .902 at third base. He improved to .260/.349/.352 with 41 runs in 61 games and a .917 fielding percentage. Coming to the US, he produced at a .277/.370/.468 clip for the GCL Cardinals, scoring 30 times in 52 games and rapping 16 doubles. He was 4th in the Gulf Coast League in doubles (between Yunior Severino and Pedro Castellanos), led with six sacrifice flies, tied Rodolfo Castro for the most extra-base hits (22) and was 3rd with 36 RBI (4 behind Ben Rodriguez and Will Robertson). Baseball America named him as the #9 prospect in the GCL, between Jonathan Guzman and Mark Vientos. 
He split a stellar 2018 between the Peoria Chiefs (.322/.381/.529, 28 2B, 15 HR, 69 RBI in 103 G) and Palm Beach Cardinals (.286/.330/.408 in 24 G). He had 37 doubles, 16 homers, 81 runs and 82 RBI on the year, fielding .890 at the hot corner. He led the Midwest League in average (.009 ahead of Vidal Brujan), slugging (.026 ahead of Moises Gomez) and OPS (5 ahead of Ryan Noda). Despite not spending a whole summer there, he was also 3rd in total bases (202, after Gomez and Chavez Young), 6th in OBP (between Taylor Wells and Jeison Rosario) and 6th in RBI (between Ryan Costello and Hunter Hargrove). He was among the Cardinals minor league leaders in doubles (1st, 7 ahead of Edmundo Sosa), runs (3rd, 3 behind Lane Thomas and Tommy Edman), hits (151, 2nd, 5 behind Edman), homers (8th, between Nolan Gorman and Patrick Wisdom), RBI (2nd, 6 behind Thomas) and total bases (242, 2nd, 10 shy of Thomas). He was named the MWL All-Star third baseman and MVP.  The last MWL MVP from the Cards chain had been Albert Pujols.  Baseball America named him the #9 prospect in the MWL, between Jeter Downs and Luis Patino. 
Baseball America named him the #5 Cards prospect entering 2019.  It was a rough year; he hit .188/.235/.317 in 59 games for the Springfield Cardinals while battling a sprained wrist and a broken hamate bone.  He hit .200/.333/.300 for the Arizona Fall League's Glendale Desert Dogs. Despite the rough summer, he made the Dominican squad for the 2019 Premier 12. He was 2 for 6 with a run as a backup 3B/DH (Jeison Guzman started at 3B). His hits were off Mexico's Eduardo Vera and the Netherlands' Orlando Yntema.  Baseball America had him as St. Louis's #10 prospect going into 2020.  However, he was unable to play at all that year because of the shutdown of the minor leagues by the COVID-19 pandemic.
On February 1, 2021, he was one of five prospects traded by the Cardinals to the Colorado Rockies in return for 3B Nolan Arenado. It was with the Rockies that he made his major league debut on May 1, 2022, starting at DH against the Cincinnati Reds and going 2-for-4 in a 10-1 win. He was then immediately sent back to the minors as rosters needed to be trimmed down to 26 players from 28.