Stanciu began his career at Unirea Alba Iulia in 2008, and went on to represent Vaslui and Steaua București in his country, winning six domestic honours and making a name for himself with the latter.

After winning a Belgian national title and a Super Cup, Stanciu joined Sparta Prague one and a half years later for another internal record fee, worth around an initial €4.5 million.

[10][11] On 20 March 2011, Stanciu scored his first goal for Unirea in a 3–0 success over Petrolul Ploiești, and he also wore the captain's armband in the closing stages of the match following Adrian Câmpeanu's substitution.

[17] Due to a transfer ban, "the Yellow-Greens" were initially unable to register the player and fellow league teams Dinamo București and Astra Ploiești tried to sign him.

On 27 March 2013, Steaua București announced the signing of Stanciu for an undisclosed fee, rumoured to be worth €700,000, with the player agreeing to a five-year deal and a €20 million buyout clause.

[22] He played all twelve matches in the 2013–14 edition of the UEFA Champions League, scoring in the 2–2 away draw against Legia Warsaw in the play-off round which assured qualification to the group stage.

[36] Stanciu made his debut in the Belgian First Division A on 11 September 2016, starting in a 3–2 home victory over Charleroi and receiving a standing ovation as he was substituted in the 85th minute by Olivier Deschacht.

[42] Stanciu ended his first season in Brussels with eight goals and eight assists in all competitions, as the team won the national championship and subsequently qualified for the next year's Champions League group stage.

[45] Stanciu underwent a medical at Sparta Prague on 18 January 2018,[46] and five days later penned a three-and-a-half-year deal for an undisclosed fee,[47] rumoured to be worth a Czech record €4.5 million.

[55] He recorded his debut in the Saudi Professional League on 7 February, in a 4–2 away win over Al-Hazem,[56] and scored his first goal nine days later in a 2–2 Arab Club Champions Cup draw with Al-Wasl.

[57] Amid financial issues at Al-Ahli,[58] Slavia Prague acquired a reported 65% of Stanciu's economic rights for €4 million, with the player signing a four-year contract on 4 July 2019.

Stanciu earned his first cap for the full side on 23 March 2016, playing the second half of a friendly with Lithuania and netting the game's only goal at the Stadionul Marin Anastasovici.

[3] On 17 May, he was picked by manager Anghel Iordănescu for his preliminary 28-man UEFA Euro 2016 squad, and eventually made it to the final list after scoring four goals in only five friendly games.

[2][68] He was awarded the number 10 shirt at the tournament in France,[69] and started in the opener against the hosts, gaining a second-half penalty that was converted by Bogdan Stancu in an eventual 2–1 loss;[70] his other appearance was against Albania (90 minutes), the 0–1 defeat leading to group phase elimination.

[71] On 4 September 2016, Stanciu assisted Adrian Popa as Romania scored their first goal of the 2018 FIFA World Cup qualifiers, in a 1–1 home draw to Montenegro where he also missed a late penalty.

He said he was protesting against a ten-match ban given to his Slavia Prague teammate Ondřej Kúdela, who reportedly racially insulted Rangers' Glen Kamara; Stanciu believed evidence was insufficient.

"[82] In the months following his national team debut, Romanian press drew comparisons between Stanciu and former internationals Gheorghe Hagi and Adrian Mutu, both of which were highly regarded by him.