Martínez played as a defensive midfielder and began his career at Real Zaragoza, with whom he won the Copa del Rey.

In 2007, Martínez began his managerial career at Swansea City and led the club to Championship promotion as League One champions.

[3] On 20 June 1993, he made his debut for the first team in La Liga on the final day of the 1992–93 season in a 2–2 draw with Atlético Madrid, coming onto the pitch as a substitute for Luis Cuartero in the 55th minute.

[6] Martínez was offered the chance to move to England by Dave Whelan, Chairman of Wigan Athletic, and he signed on a free transfer on 25 July 1995, joining fellow Spaniards Jesús Seba and Isidro Díaz, who were collectively referred to as the "Three Amigos".

[9] Martínez was also at Wigan when the team won the Football League Trophy in 1999, for which he received a winners' medal despite being injured when the final was played.

[10] Released by Wigan on a free transfer at the end of the 2000–01 season, Martínez signed a three-year deal with Scottish club Motherwell in July 2001.

[11] He made only eight appearances, plus eight more as a substitute, before having his contract terminated at the end of the season, after the club had entered administration a week earlier.

[18] On 24 February 2007, he returned to Swansea City as manager on a two-year contract, replacing Kenny Jackett, who had let him go at the end of the previous season.

[21] With Martínez in charge, Swansea lost just once in eleven games, giving them a chance of clinching a play-off place on the final day of the 2006–07 season, but missed out following a 6–3 defeat at home against Blackpool.

[24][25] The 2008–09 season saw Martínez preside over Swansea's first game in England's second-tier division in 24 years, which began poorly with a 2–0 defeat away at Charlton Athletic.

Subsequently, Swansea's form improved and they lost only four games out of the next 30, including a number of key league victories against opponents such as Reading and Wolverhampton Wanderers.

[7] Martínez signed a three-year contract worth £1.5 million and was assured by Wigan chairman Dave Whelan that his job would be safe for the next three years, even if the club suffered relegation.

[32][33] Martínez explained that his decision had been a difficult one to make, but felt the opportunity to manage in the Premier League at the club where he began his English footballing career was too good to turn down.

This inconsistency set the tone for Martínez's first season in charge, with home wins against Chelsea, Liverpool and Arsenal, but also a series of heavy defeats.

[42] During the 2012–13 season, Martínez led Wigan through their most successful ever FA Cup campaign as they won it for the first time in the club's history.

[43][44] They played Manchester City on 11 May, and won 1–0 with a goal in the 91st minute from substitute Ben Watson to become the 43rd different club to win the FA Cup.

[46] On 28 May 2013, Wigan chairman Dave Whelan announced that Martínez received permission to speak to Everton about their vacant managerial position.

[48] Whelan said Everton chairman Bill Kenwright contacted him a week earlier for permission to speak to Martínez if talks broke down.

[65] Martinez's Belgians were the first European side to advance from qualifying into the 2018 FIFA World Cup after their 2–1 win over Greece.

[68][69] Under Martínez, Belgium rose to first in the FIFA World Rankings in September 2018 and remained there in February 2021, without winning a single title in many years.

[71] However, he was unable to guide Belgium to the title at Euro 2020, as the team suffered a blowing 1–2 defeat to Italy in the quarter-finals and was eliminated.

He became the coach with the most victories in the history of the Belgian national team after beating Belarus in the qualifying phase for the 2022 World Cup.

[75] Despite this, Belgium were eliminated in the group stage following a 0–2 loss to Morocco and a goalless draw with Croatia, despite having beaten Canada 1–0 in the first matchday.

[76] Martinez resigned after the Croatia match, revealing that he was planning on departing Belgium after the tournament, regardless of their World Cup showing.

[78] His first game in charge took place on 23 March in a 4–0 home win over Liechtenstein at Estádio José Alvalade in the UEFA Euro 2024 qualifiers.

[79] On 11 September, Martinez led Portugal to their biggest victory in international history by defeating Luxembourg 9–0 at home.

[84] With wins against Czechia and Turkey and a loss to Georgia, Portugal qualified for the Round of 16 as group winners, where they played against Slovenia.

[87][88][89] Following his departure to Wigan, succeeding Swansea managers were chosen to suit the style of football Martínez had developed, such as Brendan Rodgers, Michael Laudrup, Francesco Guidolin, and Graham Potter.

[94] A number of younger coaches, including Graham Potter and Chris Davies, have studied Martinez's training methods and principles for possession-based football.