Adrien Devals served as Parish Priest of the Church of the Assumption in Penang until his consecration as Bishop of Malacca on 15 April 1934, at the same church. During his tenure he introduced different Catholic religious orders into Singapore. The Carmel of Christ the King was blessed and opened by Bishop Devals on 11 May 1938 and used by the Carmelites Sisters as a monastery. The Redemptorist Fathers and Gabrielite Brothers also came to Singaapore at the invitation of Bishop Devals. The Good Shepherd Sisters established a house for girls in 1939.
The first Catholic newspaper, ‘’The Malaya Catholic Leader’’, was initiated by Bishop Devals in 1935. It served to keep Catholics informed about Catholic teachings and issues, and to strengthen their faith.
Bishop Devals’ tenure was disrupted by the Japanese Occupation of Singapore from 1942 to 1945, where there was a massive destruction of lives and property. Catholic buildings like the Bishop’s house and Sacred Heart Church suffered considerable damage from military action.
When there was a relocation of locals, mostly Chinese and Eurasians, to Bahau in Negeri Sembilan, Malaysia, Bishop Devals followed his flock there. The Catholics there set up a chapel and continued to practice their religion. The lack of basic necessities and poor health conditions caused many deaths, including that of Bishop Devals. After cutting his foot while cultivating a vegetable patch, he suffered from tetanus, and passed away soon after, on 17 January 1945.
Bishop Devals appears to have been well-respected by the Japanese authorities in Singapore, to the point that they had even sought his views on certain matters. A senior Japanese officer recalled how Bishop Devals taught them to “love our enemies”. His Requiem Mass was attended by the senior Japanese officers.