Born in São Paulo, Gabriel joined Esporte Clube Vitória’s youth setup in 2009 from Clube Atlético Taboão da Serra, after having failed trials at Grêmio Barueri Futebol and Santos FC. He made his senior debut for the former on 7 March 2010, starting in a 3–1 win at Camaçari for the Campeonato Baiano championship, his only appearance in a season in which Vitória won the state title. He made his Série A debut on 15 May, replacing Vilson in a 1–1 home draw against Flamengo.

In August 2010, Gabriel appeared in both matches of 2010 Copa do Brasil finals against Santos, but playing as a right back in a 3–2 aggregate loss. On 5 December, in the last game of a league season which saw his team relegated, Gabriel was sent off for a foul on Anaílson in a goalless home draw against Atlético Goianiense.

He made his first team breakthrough in late 2011, and went on to play a crucial role in the following year, appearing in 35 matches as Leão returned to Série A. On 6 September 2012 Gabriel signed a contract extension with Vitória, until 2016.

On 15 August 2013, Gabriel moved to La Liga outfit Villarreal, signing a five-year deal with the club. He made his debut in the competition on 10 November, starting in a 1–1 home draw against Atlético Madrid.

Gabriel featured in 18 league matches during his first season abroad, sharing terms with Chechu Dorado, as the Yellow Submarine finished sixth and subsequently returned to a European competition. He made his UEFA Europa League debut on 21 August 2014, starting in a 3–0 away win against FC Astana.

On 26 January 2015, Gabriel was granted a work permit by the UK government and expected to join Arsenal for a fee of around £11.3 million. He signed for the club two days later, with Joel Campbell moving the other way on loan. Manager Arsène Wenger stated that despite the player’s fitness, Gabriel could make errors in his first matches due to not being able to speak English.

On 19 September 2015, Gabriel was sent off at Chelsea for a tussle with Diego Costa; Santi Cazorla was later dismissed as nine-man Arsenal lost 2–0. Gabriel initially received a standard three-match suspension for violent conduct after receiving a direct red card, but the decision was later withdrawn after a “wrongful dismissal claim”; he was however banned for one match and fined £10,000 for improper conduct by not leaving the pitch immediately.

On 28 December 2015, Gabriel scored his first goal in European football, heading in Mesut Özil’s corner kick to open a 2–0 win against Bournemouth; the result put the Gunners to the top of the Premier League.

On 20 March 2015, Gabriel was called up to the Brazil national football team for the first time, replacing the injured David Luiz for friendly matches against France and Chile. However, he did not feature in either match.

On 18 August 2017, Gabriel returned to Spain to join Valencia on a five-year contract. He made his debut on 9 September, in a 0–0 home draw against Atlético Madrid. On 20 January 2018 he was sent off for dissent in a 2–1 loss at UD Las Palmas, infuriating his manager Marcelino García Toral.

Gabriel played five games as Los Che won the 2018–19 Copa del Rey, including the 2–1 final win over Barcelona on 25 May; it was their first honour for eleven years. On 10 December 2019 he was sent off at the end of a 1–0 win at AFC Ajax in the last game of the Champions League group stage, for headbutting Dušan Tadić.