[4] He received his episcopal consecration on 24 May at the Cathedral of St Stephen in Passau from the Archbishop of Munich and Freising Cardinal Reinhard Marx.

Stefan Oster chose the motto Victoria Veritatis Caritas ("The victory of truth is love").

He was pleased that the Congregation found the proposals premature and said this demonstrated that the issue could not be resolved by a national conference.

"[8] In March and April 2019, Oster gave several interviews on current topics relating to the Church and sexual issues.

He said that Christian sexual morality needs further developments in order to demonstrate that sacerdotal marriage has ceased to qualify as a sin and can be blessed in the Roman Catholic Church.

[10] In September 2019, Oster gave "a poignant address" at the end of a meeting of the German Bishops Conference that determined, despite many concerns, to proceed with a national synod.

He said a critical-minded youth probably saw scandal, an "archaic" or "crooked organization with forbidding morals and incomprehensible regulations of belief."

He lamented the Church's failure to communicate its joy because it seems crippled by "the crimes, the complacency, the absence of responsibility and holy experiences."

"[11] In March 2021, Oster was one of three German bishops to welcome the CDF's explanation of why the Church prohibited the blessing of same-sex relations.