Dangane da asusun da aka bayar a Hikayat Merong Mahawangsa (wanda kuma aka sani da Kedah Annals), an kafa Masarautar Kedah lokacin da sarki Phra Ong Mahawangsa ya musulunta kuma ya karɓi sunan Sultan Mudzafar Shah.At-Tarikh Salasilah Negeri Kedah ya bayyana musuluntar da addinin musulunci tun daga shekara ta 1136 miladiyya.Duk da haka, ɗan tarihi Richard Winstedt, wanda ya ɗauko labarin Acehnese, ya ba da kwanan wata 1474 na shekarar da sarkin Kedah ya musulunta.Wannan kwanan wata ya yi daidai da wani rahoto a cikin Malay Annals, wanda ke bayyana raja na Kedah da ya ziyarci Malacca a lokacin mulkin sarkinta na ƙarshe yana neman girmamawa ga ƙungiyar masarautar da ke nuna ikon mallakar wani shugaban musulmi na Malay.Buƙatun da Kedah ya yi ya kasance a mayar da martani ga zama vassal Malacca, mai yiwuwa saboda tsoron zaluncin Ayutthyan.^[76] Jirgin ruwan Burtaniya na farko ya isa Kedah a cikin 1592. ^[77] A cikin 1770, Kamfanin British East India Company (BEIC) ya umurce Francis Light ya dauki Penang daga Kedah.Ya cimma hakan ne ta hanyar tabbatar wa Sarkin Musulmi Muhammad Jiwa Zainal Adilin na biyu cewa sojojinsa za su kare Kedah daga duk wani hari na Siyama.A sakamakon haka, Sarkin ya amince ya mika Penang ga Birtaniya.