He received his episcopal consecration on 13 February 1938 from Archbishop Jean-Alexis Chambon, MEP, with Bishops Paul Aijiro Yamaguchi and Marie-Joseph Lemieux serving as co-consecrators.

During World War II, Doi served as executive director of the National Catholic Central Committee.

Pope John XXIII created him Cardinal Priest of S. Antonio da Padova in Via Merulana in the consistory of 28 March 1960.

[4] He attended the Second Vatican Council from 1962 to 1965, and was later one of the cardinal electors who participated in the 1963 papal conclave that selected Pope Paul VI.

Doi, along with Stefan Wyszyński, assisted Paul Peter Meouchi in delivering one of the closing messages of the Second Vatican Council on 8 December 1965.