Andreu spent his early career in France and Switzerland with Monaco, Chênois and Stade Nyonnais. While playing in Switzerland, Andreu started writing poetry; he is also a fan of books, stating "I have a lot of free time. I love to read – whether it is thrillers, crime stories or more philosophical themes – and I recently bought a book about French history. I sometimes write poems and I note down details about the books I've read."
Livingston
He signed for Scottish club Livingston in June 2012, alongside David Luongo. It was revealed by John Hughes that the director of footballJohn Collins signed the duo, with the help from Collins' French connections by inviting them on trial, which impressed Hughes' management. He made his debut for Livingston in the first round of the Scottish Challenge Cup, in a 1–0 loss against Annan Athletic. Andreu scored his first goal in the closing minutes of the match as they beat Falkirk on 2 September 2013. On 2 March 2013, Andreu scored twice in a 4–1 win over Airdrieonians. In a BBC Scotland interview, Andreu's name was mentioned by the UEFA general secretary, David Taylor. On 2 May 2013, it was announced that he was leaving the club at the end of the 2012–13 season. While at Livingston, Andreu met Julia, daughter of then director of football John Collins and they entered into a relationship.
Hamilton Academical
He signed a one-year contract with Hamilton Academical on 1 August 2013, having appeared for the club in the Scottish Challenge Cup a few days earlier as a trialist. He signed a new two-year contract with the club in March 2014. In April 2014, he was nominated for the 2013–14 PFA Scotland's Player of the Year award in the Championship section, but lost out to Hemmings. He was also selected to the 2013–14 Championship PFA Scotland Team of the Year, alongside Hamilton teammates Ziggy Gordon and Ali Crawford. In the last game of the season, Andreu scored a hat-trick in the first half as they thrashed Greenock Morton. However, the win wouldn't guarantee promotion after Dundee also won on the same day. He scored the winning goal in the promotion play-off semi-final against Falkirk on 18 May 2014. After losing 2–0 to Hibernian in the first leg, Andreu scored a last minute goal in a 2–0 win at Easter Road to level the tie on aggregate. Hamilton won 4–3 in a penalty shoot-out to relegate Hibernian and achieve promotion to the Premiership. After the match, Andreu described playing in the Scottish Premiership in the 2014–15 season as "a dream come true" and said the club deserved to be promoted.
Norwich City
He moved to English club Norwich City on 2 February 2015.
Rotherham United (loan)
Andreu moved on loan to Rotherham United on 1 September 2015. On 26 September, he scored his first goal for Rotherham in a 2–0 win over Birmingham City. On 7 January 2016, he returned to Norwich City to fight for his place in the first team, despite Rotherham manager Neil Redfearn's wishes to extend the loan.
Dundee United (loan)
He signed on loan for Dundee United in August 2016. On his debut he scored the winning goal in a Scottish Challenge Cup tie against Peterhead on 3 September 2016.
Coventry City
On 10 August 2017, Andreu left Norwich City by mutual consent. On the same day he signed a two-year contract with Coventry City. He scored his first goal for Coventry in an EFL Trophy tie against Shrewsbury Town on 29 August 2017. During Coventry's 1-0 win against Port Vale on 9 September 2017, Andreu suffered an injury to his anterior cruciate ligament which would rule him out for the rest of the 2017–18 season. He returned to Hamilton on loan in January 2019.
St Mirren
On 4 July 2019 Andreu signed for St Mirren on a one-year deal after being released by Coventry City. On 2 June 2020 it was announced that he would remain with the club under the coronavirus furlough scheme before leaving the club.
Playing style
Andreu's playing style has been compared to Cesc Fabregas.
