After starting out in the Madureira youth system in his home country, he joined Uruguayan club Deportivo Maldonado, but later returned to Brazil and made his professional debut with Vasco da Gama in 2009.

Allan was signed from Madureira by Uruguayan side Deportivo Maldonado at 17 years of age [citation needed] for an undisclosed fee.

He then returned to action in the last round of the Série A before the break for the 2011 FIFA U-20 World Cup, playing in the Copa da Hora friendly tournament.

[5][6] He made his debut for Udinese at home at the Stadio Friuli against Juventus, where he created an assist for teammate Andrea Lazzari's goal.

[12] Allan would then receive a start in Napoli's third game of the season, a 2–2 away draw with Empoli, scoring an equalizer in the 78th minute after converting a pass from captain Marek Hamšík.

[14] Allan would go on to score once again and provide another assist in a 5–0 win against Lazio, only three days after the Brugge victory on 20 September, giving manager Maurizio Sarri trust in him for his precise passing and defensive work.

[15] On 26 September, Allan scored a goal against defending champions Juventus, with excellent passing and an impressive overall game in a 2–1 home win.

In the 2019–20 season, he played in the 2019–20 UEFA Champions League round of 16 home match against Barcelona, which ended 1–1, then he won the 2019–20 Coppa Italia against Juventus, his only silverware with Napoli.

[19] On 5 September 2020, English club Everton signed Allan for around £21.7m on a three-year deal, to be reunited with former Napoli manager Carlo Ancelotti.

[25] He was called up by Brazilian under-20 coach Ney Franco on 20 August 2011, where he impressed enough at Vasco da Gama to earn a call-up for the 2011 FIFA U-20 World Cup.

Brazil's U-20 World Cup-winning side also featured the likes of Oscar, Philippe Coutinho, Casemiro and Danilo, as well as future Napoli teammates Gabriel and Bruno Uvini.

Sky Sport Italia and TV Luna report that he has been asked 'to switch allegiances to the Azzurri' by national coach Roberto Mancini.