Turkish media outlet Hurriyet claim that the club’s sporting director Ceyhun Kazanci has agreed terms with Ismael with the move now just requiring club President Ahmet Nur Cebi’s final approval.
The Frenchman was sacked by West Brom at the start of February after just seven months in charge.
Kazanci said: “I agreed with Valerien Ismael on every issue. There is no problem about the time. If our President approves, he will immediately take over the team.”
Both Kazanci and Cebi are said to have agreed on Ismael taking charge of Besiktas, but Cebi wants to ‘discuss the issue with the whole team one last time’.
Ismael left Barnsley last summer after taking them into the Championship play-offs last term - after only arriving at Oakwell in the autumn of 2020.
Assistant head coach Adam Murray, head of sports science Jonny Northeast and video analyst Jack Riley all followed him to the Hawthorns.