Aga Syed Mustafa went to Hawza 'Ilmiyah Najaf, Iraq for higher studies to fulfill his late father's wish.

After returning to Kashmir Aga Syed Mustafa worked as the deputy of his uncle and helped him in the religious affairs.

In Kashmir he headed the Sharia Court founded by Ayatullah Aga Syed Mehdi Sarkaar over 100 years previously.

[7] After the death of Imam Khomeini in 1989, Aga Syed Mustafa introduced Ayatullah Ali Khamenei to the people of Kashmir as Wali-Amr-al-Muslimin.

After this incident, Ali Khamenei invited Aga Sahab to the Islamic Republic of Iran to show empathy and offer condolences.

Abu Shaheedain Aga Syed Mustafa[11] died on 21 August 2002 due to prolonged illness,[12] according to official reports hundreds of thousands of people attended the funeral prayer at Budgam.