[1] A strong advocate for English-language education, he also championed the strict enforcement of Islamic laws, including the prohibition of alcohol consumption for Muslims and the regulation of Khalwat violations.

[2] Pengiran Muhammad Salleh, a member of the Tujuh Serangkai, was highly regarded for his fluency in Quranic recitation and deep knowledge of royal customs, as described by Sultan Omar Ali Saifuddien III in Syair Perlembagaan Negeri Brunei.

As part of the committee, Pengiran Muhammad Salleh played a key role in compiling public feedback and constitutional analysis into a fifty-page report, which was submitted on 23 March 1954[7] and received an unexpectedly positive response from the authorities.

[2] On 14 March 1959, during the absence of the sultan, who travelled to London to negotiate a written constitution for Brunei, he and Pengiran Muda Hashim were appointed as regents and began their duties, a role they had previously undertaken several times.

[13] The following month, he was appointed to both the MUIB and the Adat Istiadat Council, which were established to oversee matters related to religion, customs, and the state court.

He was one of the 20 individuals appointed, with his role as chairman of the newly formed MUIB on 15 October marking the council's creation to align religious laws and governance with the new constitution, succeeding the Sultan's previous position as its chair.

[18] The following month, he was again appointed to the Regency Council, alongside wazirs, ministers, and LegCo members, to oversee the sultan's duties during his holiday in Malaya.

The funeral procession began at 11:00 a.m. from the Pengiran Muhammad Salleh's residence, accompanied by various royal and government officials, including the sultan, the British high commissioner, and other dignitaries.

[24][5] His final promotion came in the form of the wazir title Pengiran Di-Gadong Sahibul Mal,[b] which was conferred at the Lapau on 9 May 1968,[1] and styled as Yang Teramat Mulia Seri Paduka.