He earned his first senior cap in 2019 UEFA Nations League Finals, winning the inaugural edition of the competition on home soil.

Félix started playing football at Os Pestinhas in 2007 before joining the youth ranks of FC Porto a year later at age eight.

[9] Félix was released by Porto in 2014 because of his slight frame (he denied these claims and said he left of his own volition)[10] and moved to Lisbon rivals Benfica in 2015, at age 15, after a season-long loan at Padroense.

[11][12][13] Félix debuted professionally at age 16 for Benfica's reserve team in LigaPro on 17 September 2016, as an 83rd-minute substitute for Aurélio Buta in a goalless draw at Freamunde.

[17] During that season, Félix played in the 2016–17 UEFA Youth League, in which he was a key part of Benfica reaching the final of the competition, which it lost to Red Bull Salzburg (2–1), scoring six goals in the tournament.

[20] After Bruno Lage took over as coach of Benfica, his first decision was to use Félix more regularly, partnering him with Haris Seferovic in the attack, taking advantage of the bad run of Facundo Ferreyra and Nicolás Castillo and the injury of Jonas.

[21] Later on, Félix was praised for his performance in a 4–2 away win over Sporting CP in the league on 3 February,[22] subsequently sparking interest from several European clubs.

[23] A month later, he scored the equaliser in a 2–1 away comeback win over Porto in the O Clássico, allowing his side to overtake their rivals at the top of the Primeira Liga table.

[35] Despite not scoring a goal, he managed to win a penalty for Atlético after being fouled inside the box which Álvaro Morata subsequently failed to convert.

[40] On 19 October, Félix suffered an ankle injury against Valencia, after a rash challenge by Dani Parejo, leaving his team with only ten men on the pitch, as his coach Diego Simeone had already made the maximum number of allowed substitutions.

[51] On 23 January, Félix made his Copa del Rey debut in the Round of 32, providing an assist for Ángel Correa in a 2–1 loss against Cultural Leonesa.

[54] On 11 March 2020, during extra time in the second leg of Atlético's tie against Liverpool, Félix provided an assist for Marcos Llorente in an eventual 3–2 away win, which saw his team qualify to the quarter-finals of the competition.

[56] On 13 August, Félix was substituted on in the second half against RB Leipzig in the Champions League quarter-finals, winning and converting a penalty to equalise for Atlético; the match would end in a 1–2 defeat that saw his side exit the competition.

[65] On 16 May, the penultimate matchday of the La Liga season, Félix provided a crucial assist to Renan Lodi of his side's 2–1 comeback victory over Osasuna, to ensure that Atlético would remain on top of the table.

[67] At the end of the season, he had made 31 league appearances, scoring seven goals and providing six assists, as Atlético won their first La Liga title in seven years.

[69] On 18 September, Félix was sent off in the 78th minute in a 0–0 home draw against Athletic Bilbao, for calling the referee "crazy", leading him to receive a two-match ban.

[75] After suffering a hamstring injury following a league against Osasuna on 20 November, Félix began falling out with manager Diego Simeone, losing his place as a starter.

[83] The following match, on 23 February, Félix scored Atlético's opening goal in a 1–1 home draw over Manchester United at the first leg of Champions League round-of-16 tie.

[84] In the reverse fixture, on 15 March, Félix created Renan Lodi's goal, which was assisted by Antoine Griezmann, to help Atlético defeat Manchester United 1–0 at Old Trafford and qualify to the quarter-finals, securing a 2–1 aggregate win.

[88] Félix started the 2022–23 season, on 15 August, providing a hat-trick of assists for the first time in his career as Atlético beat Getafe 3–0 away from home.

"[95] On 11 January 2023, Félix joined Premier League club Chelsea on loan for the remainder of the 2022–23 season, extending his contract with Atlético to 2027 before the move.

[99] After scoring four goals in 20 appearances, Atlético's president Enrique Cerezo confirmed that Chelsea's new head coach, Mauricio Pochettino, did not want the club to sign Félix on a permanent deal following the expiration of his loan.

[119] At the reverse fixture at Metropolitano, on 17 March, Félix opened Barcelona's 3–0 victory over Atlético Madrid, helping his side move to the second spot in the La Liga table.

[125] On 14 June 2017, Félix began his international career with Portugal's under-18 team, debuting against Norway, replacing Elves Baldé in the 58th minute.

On 10 October 2017, Félix debuted for Portugal's under-21 team for the qualification of the 2019 UEFA European Under-21 Championship, in a 3–1 defeat against Bosnia and Herzegovina, replacing Xadas in the 56th minute.

[132] On 15 March 2019, manager Fernando Santos called up Félix to the senior team for the first time, ahead of the opening UEFA Euro 2020 qualifying matches.

[145][146] On 11 September 2023, Félix scored the closing goal as Portugal defeated Luxembourg 9–0 at home in the UEFA Euro 2024 qualifiers, the biggest win in the team's history.

[152] A technical gifted and intelligent player, with an eye for goal, his primary traits are his creativity, finishing, touch on the ball, and dribbling skills, as well as his vision and precise passing.

[150][22] His playing style has led him to be compared to Brazilian former playmaker Kaká and former Benfica players Rui Costa and João Pinto;[150][22] he has also been likened by some in the media to compatriot Cristiano Ronaldo,[149] as well as former Atlético Madrid forwards Sergio Agüero and Antoine Griezmann.

[155][156] Regarding Félix's playing style in 2019, Rui Costa praised the youngster for his "understanding of the game," and his "ability to know where to be in front of goal.