In 1990, he joined Messrs. Hisham, Sobri & Kadir where he is presently the Principal Partner. His main areas of practice are corporate and commercial law and Islamic banking and finance. Tengku Dato Seri Hasmuddin is among the legal counsel involved in framing the structural framework for Islamic banking documentation in the early stages of that sectors development in Malaysia. He is a member of the Chartered Institute of Islamic Finance Professional since 2009. He continues to play an active role in the development of this area of law through his involvement in the organization of Kuala Lumpur Islamic Finance Forum (KLIFF), an annual forum that gathers prominent personalities, practitioners and industry players of Islamic Finance as well as by presenting papers on the subject both locally and internationally. 
 
Tengku Dato Seri Hasmuddin was the former director of Bank Muamalat Malaysia Berhad. He was appointed as a Non-Independent Non-Executive Director of Bank Muamalat on 18 April, 2006 and was subsequently redesignated to Independent Non-Executive Director by Bank Negara Malaysia on 16 February, 2009 until his retirement on 18th April, 2018.  He is also the former director of  Rangkaian Hotel Seri Malaysia Sdn. Bhd., Institut Jantung Negara Sdn Bhd, Amanah Ikhtiar Malaysia and Serba Dinamik Holdings Berhad.

Currently Tengku Dato Seri Hasmuddin sits on the boards of  IJN Holdings Sdn Bhd, Aliran Ihsan Resources Berhad and Lembaga Tabung Haji. 

Tengku Dato Seri Hasmuddin is also involved in charitable organisations in his capacity as trustee to Tuanku Najihah Foundation, Yayasan Institut Al Quran Kuala Lumpur, Tabung Amanah Pesakit Malaysia, Institut Quran Tuanku Jaafar and Yayasan Munarah.

1.  Aliran Ihsan Resources Berhad

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