After not playing a single game for Barcelona in the 2017–18 season, Arda was loaned out to Turkish club İstanbul Başakşehir for the remainder of the season and two more, in the winter transfer window. He made his debut for the club in a league match on 21 January 2018, coming off the bench in the 65th minute mark and scoring the third goal in the 3–0 away win over Bursaspor. On 4 May 2018, Turan was sent off in a league match against Sivasspor for pushing an assistant referee after disagreeing with a ruling. He received a 16-match ban from the Turkish Federation's disciplinary board, the longest punishment ever issued to a player in the country. Later, however, the ban was reduced to 10 games by TFF's arbitration board. On 7 January 2020, Turan's loan was terminated six months early by Başakşehir.
He was granted his 100th international appearance for Turkey in the 3–0 defeat to Iceland national football team in 2018 World Cup qualifying group match in October 2017.
Turan married Aslıhan Doğan on 11 March 2018. President of Turkey Recep Tayyip Erdoğan attended the wedding where he was acting as a witness of the marriage. In October 2018, the couple's first child, a son named Hamza Arda, was born. Another son named Asil Aslan was born in June 2020.
Arda Turan received a suspended sentence of 2 years and 8 months after being found guilty of firing a gun to cause panic, illegal possession of weapons and intentional injury. Turan got into a brawl with Berkay Şahin in 2018 which ended with a broken nose for the pop star. Turan appeared at the hospital with a gun, allegedly begging for forgiveness from Şahin, panic ensued after the footballer fired the weapon at the ground. Turan will not serve his jail term if no further incidents occur for five years.