[4] As a professional, Montero started his career for Peñarol in 1990 and remained with the club for two seasons, making 34 appearances and scoring one goal before transferring to Atalanta in the Italian Serie A in 1992.

After impressing greatly during his four-year stay in Bergamo, Montero made the highly anticipated switch to the Italian and European powerhouse, Juventus.

[4] Juventus were extremely dominant both domestically and internationally during this period and had what was considered to be the best defence in the world at the time, and teams strongly regretted ever going down a goal to the club, as they knew how hard it would be to score one back for themselves.

In the 2003 UEFA Champions League final, Montero was one of the three Juventus players to have their penalty saved by AC Milan keeper Dida in the shootout defeat.

An important member of the Uruguayan national side, Montero first represented his team in an international tournament at the 1997 FIFA Confederations Cup, finishing in fourth place.

Sadly for Montero, he limped off with a hamstring injury during the second game in Sydney, and later, Australia went on to narrowly snatch the win and the World Cup qualification via penalties.

After the defeat, Montero immediately announced his international retirement, saying "what happened today was such a pity as this group of players deserved to be at the World Cup finals.

[11] Considered to be one of the best defenders of his time, and one of Juventus's greatest ever centre-backs, Montero has been described as "skilful on the ball and calm under pressure",[12] and a "wonderfully talented and intelligent footballer".

[4] A versatile defender, he was capable of playing in the centre (both as a stopper or as a sweeper) or on the left (although this was not his favoured position), and was known for his strength, consistency, leadership and organisational skills.

[14][15][16][17][18] A combative, tenacious, complete and talented defender,[19] he was also frequently criticised for his aggression and hard tackling playing style throughout his career,[19] as well as his knack for picking up unnecessary bookings.

[24] Welsh former winger Ryan Giggs described Montero and his defensive teammate at Juventus Ciro Ferrara as "...the toughest defenders [he] played against", also adding that they were often very hard in their challenges.

[25] After retirement, Montero embarked on a career as a manager, working in his native Uruguay with Peñarol, and in Argentina with Boca Unidos, Colón, and Rosario Central.