[8] Upon arrival, Gameiro was inserted onto the club's reserve team in the Championnat de France Amateur, the fourth level of French football.

[9] In 2005, with Duguépéroux now managing the team, Gameiro made his professional debut on 10 September 2005 in a match against Paris Saint-Germain appearing as a substitute in the 59th minute of a 1–0, Ligue 1 defeat.

[10] On 14 December, Gameiro made his European debut in a UEFA Cup match against Serbian club Red Star Belgrade.

The stalemate ensured Strasbourg won the group and the team later advanced to the Round of 16 where they suffered elimination losing 4–2 on aggregate to Swiss club FC Basel.

[14] Three weeks later, his season was cut short after rupturing ligaments in one of his knees following a tackle from Troyes midfielder Blaise Kouassi.

[15] The injury required six months of rehabilitation, which resulted in Gameiro missing the Coupe Gambardella competition, which the Strasbourg under-19 team won, defeating Lyon 3–1 in the final at the Stade de France.

He only scored two goals, against Gueugnon and Istres, again, for the rest of the season as Strasbourg achieved promotion back to Ligue 1 courtesy of the club's 3rd-place finish.

[32][33] Gameiro continued his consistency during the spring portion of the season scoring goals against Sochaux, Grenoble, Marseille, and Nancy.

On 27 January 2010, Gameiro scored the only goal in Lorient's upset victory over Lyon in the Coupe de la Ligue.

Despite the reported agreement, Lorient president Loïc Féry declared that while personal terms had been agreed, Valencia had never sent in a transfer fee offer for the player.

Beginning in late January, he proceeded to go on a tear scoring seven goals in the team's four ensuing league matches.

[58] On 10 June 2011, media reports confirmed that Paris Saint-Germain had reached an agreement with Lorient for the transfer of Gameiro.

[60] Gameiro agreed to a four-year contract and the transfer fee was priced at €11 million with future bonuses to be added later.

[61] Gameiro made his competitive debut for Paris Saint-Germain on 6 August 2011 in the team's opening 1–0 league defeat to Lorient.

On 18 August 2011, in Paris Saint-Germain's first leg UEFA Europa League playoff round tie against Luxembourger club Differdange, Gameiro scored the opening goal for the team in a 4–0 away win.

Gameiro scored on 20 January, against Sablé-sur-Sarthe FC in Coupe de France play, 4 February, against Evian TG, and 11 March, against Dijon FCO.

[citation needed] Gameiro's first goal in the 12/13 campaign came 29 September 2012 against FC Sochaux, coupled with a second 22 minutes later.

[citation needed] Given that Gameiro was transferred in the offseason, this occasion marked both his last scoring performance and last match for PSG.

On 25 July 2013, Gameiro signed a contract with Sevilla for a fee of €10 million, agreeing to a five-year deal for the Ramón Sánchez Pizjuán club.

[69] Gameiro scored his first goal for the Spanish side in their first-leg Europa League play-off tie against Śląsk Wrocław, a 4–1 home win on 22 August.

[70] On 1 September, Gameiro achieved a brace against Málaga CF, including a header, but this failed to bring victory to his side as the match ended in a 2–2 draw.

[71] Following this, Gameiro scored on five occasions, including a 1 December contest against Granada CF, in which he also garnered a yellow card.

[75] In the 2013–14 La Liga Seville derby against Real Betis three days later, Gameiro scored twice more to give Sevilla a 2–0 away victory.

[76] In the final of the 2013–14 Europa League against Portuguese side Benfica on 14 May 2014, Gameiro came off the bench in extra time and scored the game-winning penalty kick to secure a 4–2 shoot-out victory for Sevilla.

[81] On 18 February 2017, Gameiro scored the fastest La Liga hat-trick in over 22 years, coming on a substitute in the 62nd minute in the match against Sporting de Gijón in a 4–1 victory.

Gameiro was called up for the under-21 team's 2009 UEFA European Under-21 Football Championship qualification play-offs tie against Germany, but did not feature in either leg.

Due to having Portuguese heritage through his paternal grandfather, Gameiro was eligible to represent Portugal at the senior international level.

In 2009, then-manager Carlos Queiroz declared that Gameiro was "an interesting player" and that he "would love to talk to him" regarding representing Portugal.