Originally from Villaviciosa, a small town in Asturias, in Northern Spain, Marcelino trained in the lower categories of Sporting de Gijón. He made his debut with the first team on December 22, 1985, in a 1-1 draw at home against RC Celta de Vigo. In Sporting he played four seasons, participating in a total of 86 games.
After two seasons with Racing Santander and Levante UD, MGT ended up at Elche CF, where he retired prematurely in 1994 at the age of 28 due to a knee injury.
MGT was regularly called up to play with the lower categories of the national team. Between the U18 and the U21, he added 25 caps, reaching the final of the 1985 U-20 World Cup.
He began training at the age of 33 with the humble CD Lealtad, a Third Division team in Asturias with which he achieved promotion to Second B. At the beginning of the 2000s he joined the club where he had made his debut as a footballer: Sporting de Gijón.
For two years he headed the Sporting de Gijón first team, finishing fifth and tenth in the Second Division, with a group of young players and one of the lowest budgets in the league.
In the summer of 2008, Real Zaragoza in the Second Division trusted MGT to return the club to the First Division. The bet was a success and the goal was achieved that same season.
After his second stage in Santander, Sevilla FC signed MGT in the summer of 2011. Despite a good start, the course of the season changed and in February 2012 he was dismissed. Both Marcelino and key leaders of the Sevilla club agreed that there had been failures by both parties and both assumed their responsibility.
In January 2013 MGT started a fantastic journey with Villarreal CF, in Second Division. The first success was to return the team to First Division. In the following three seasons, they managed to finish the league in the top six, including a fourth place and qualification for the UEFA Champions League.
In addition, during this stage he reached two semi-finals: one in the Copa del Rey and another in the UEFA Europa League, where he even won the first leg against Jurgen Klopp’s Liverpool.
On May 11, 2017, Valencia CF announced his hiring as the team’s coach from the 2017-18 season in which he achieved a fourth place and qualification for the Champions League.
A season later, he repeated the fourth position in the League and was proclaimed champion of the Copa del Rey after beating FC Barcelona in the final and obtaining a new title for the Valencian club 11 years after their last success in this competition.
However, at the beginning of the 2019-20 season, Peter Lim decided to dispense with the services of the Asturian coach.
MGT arrived at Athletic Club on January 4, 2021. After 12 days in his current position, he won the Super Cup semifinals against Real Madrid. 3 days later he won the second title of his career, the 2021 Super Cup, beating FC Barcelona in the final. He reached the Supercup final again in 2022 after beating Atlético but this time he could not win the trophy against Real Madrid.
In the league his team finished in the eighth position, with 55 points (9 more than the previous one). That is the best score of the Athletic Club in its last five campaigns. In Copa del Rey he was one step away from the final after winning Barcelona and Real Madrid consecutively.
In November 2023, seven years after his first spell, Villarreal calls Marcelino again to lead a project. ‘Let’s get excited again’ wishes the club, which trusts the MGT coaching staff until June 2026.