On 18 December 1972, Pope Paul VI appointed Kitbunchu the second Archbishop of Bangkok. He received his episcopal consecration on 3 June 1973 from Archbishop Joseph Khiamsun Nittayo, with Bishops Lawrence Thienchai Samanchit and Michel-Auguste–Marie Langer, MEP, serving as co-consecrators. He served as President of the Thai Episcopal Conference from 1979 to 1982, and again from 2000 to 2006.[2]
During the 2006 political crisis in his Thailand, Kitbunchu called for unity, saying, "All Thai people are patriotic and want the country to progress and develop on all fields, but now the political crisis has disturbed and worried the people." He also asked Thais to "correct what is wrong and forgive each other."[5]
Kitbunchu resigned from his position as Archbishop of Bangkok on 14 May 2009. At the time of his retirement, he was the oldest active head of an archdiocese in the Latin Church. In addition to his native language, Central Thai (official and national) and his ethnic Chinese dialect of Teochew, he can also speak other languages such as Latin, English, Italian, French and Standard Mandarin.[2]
He is tied with Alexandre do Nascimento as the longest-tenured member of the College of Cardinals, having been appointed in 1983, positions they have held since the death of Roger Etchegaray in 2019.