Mr Sayeed played a key part in Nomura's acquisition of Lehman Brothers' operations in the Middle East and Europe in 2008 and has been praised by the bank for his role in bringing about a "remarkable transformation" in Nomura's fortunes in the two markets.
Takumi Shibata, chief operating officer and deputy president of Nomura Holdings, said: "We are very grateful for all that Sadeq has achieved in the last ten years and especially in the past 18 months."
Mr Sayeed is to remain in his post until a suitable candidate is found to replace him.
His departure follows the loss of two other executives from the company.
Earlier this month, Siggi Thorkelsson, head of equities for Asia, and Thomas Siegmund, co-head of fixed income in the same region, announced they would both be leaving Nomura.
By Tony Aynsley