After further studies, he was designated as Kota Belud District Officer. He also held some positions in the Cabinet of Sabah. In many years, he was the Minister of State for Finance, Minister of State for Local Government and Housing and Deputy Chief Minister of State. On 28 December 1994, Prime Minister Mahathir Mohamad appointed him as the Chief Minister of the State. His tenure as the State Chief Minister ended on 26 May 1996, and he was succeeded by Sabah Progressive Party President Yong Teck Lee. On 4 January 2010, Chief Minister of State, Musa Aman, appointed him as his Science and Technology Adviser with ministerial rank. He replaced Tham Nyip Shen, former Deputy Chief Minister of State. On 12 January 2011, he was appointed as the Speaker of the State Legislature. Before that, on the first day of 2011, he was appointed as the Chairman of National Film Development Corporation Malaysia by the Federal Minister of Information, Communication and Culture, Dr. Rais Yatim. Under the party of United Malays National Organisation, he is the Sabah Liaison Deputy Chairman. He also presides over the United Sabah Bajau Organisation. On 6 October 2019, on the same day of the large-scale Malay Dignity Congress that was attended by the leaders of the five main Malay political parties in Malaysia, United Malays National Organisation, People's Justice Party, Malaysian Islamic Party, Malaysian United Indigenous Party and National Trust Party, including Prime Minister, Leader and Chairman of the ruling Pakatan Harapan and Malaysian United Indigenous Party, Dr Mahathir bin Mohamad and other leaders from the respective parties. He admitted that he is submitting the admission letter to the People’s Justice Party as the party is multiracial, and it is in line with Salleh's political beliefs, especially focusing on the future of the Malaysian state in East Malaysia, Sabah. On 30 June 2020, he canceled his application to join PKR after thinking deeply and taking into account today's political landscape including PKR's internal turmoil. He said, the decision was made last April and with the cancellation he remained non-partisan since leaving UMNO in 2018. Previously, Salleh applied to join PKR in October last year.
Election results
Awards
After his appointment as the chief minister of Sabah, he received award of the Grand Commander of the Order of Kinabalu, which carry the title of "Datuk Seri Panglima".
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* Grand Commander of the Order of Kinabalu - Datuk Seri Panglima
Family
He is married to Datin Seri Panglima Datuk Raya Erom on 18 December 1985 and has two sons and two daughters. The names of his children are, Mohd Syarulnizam, Syazeera, Mohd Hafeez and Syeera. Salleh is also the second cousin of Isnaraissah Munirah Majilis.