Zahir Mosque, built in 1912 was contributed by YTM Tunku Mahmud Ibni Almarhum Sultan Tajuddin Mukarram Shah. The site of this mosque was once the cemetery for fallen Kedah warriors who fought defending Kedah from Siam (1821). Zahir Mosque is one of Kedah's most distinctive architectural landmarks, standing as an elegant example of Malay-Islamic architecture.

As one of the oldest mosques in the country, the design of Masjid Zahir is based on that of Masjid Azizi of Bandar Langkat in northern Sumatra. The mosque has five domes to represent the five tenets of Islam. Sultan Abdul Hamid Halim Shah officiated the opening of Masjid Zahir on Friday, 15 October 1912.

Located in central Alor Setar, it is the official mosque for the state as well as the main mosque for local Muslims and the venue for the annual Koran reading competition.

The Zahir Mosque occupies a site of approximately 124,412 sq.ft. Its centre hall (prayer hall) measures 62 x 62 sq.ft and is surrounded by verandahs with 4 mezzanine areas, each with its own dome. The main dome is located at the northeast of the mosque building.