[1] As auxiliary bishop, he was given responsibility for the north of the archdiocese, including the cities of Düsseldorf and Wuppertal,[3] and was episcopal vicar for the doctrine of the faith and ecumenism, as well as being in charge of the permanent diaconate.

[3] Woelki has been criticised by some German politicians for his language on homosexuality, which has led them to question his suitability for the post of archbishop in a city with a significant gay population.

[10] He was created Cardinal-Priest of San Giovanni Maria Vianney, becoming the youngest member of the College of Cardinals, in succession to Reinhard Marx of Munich.

He was praised by the group for speaking out in favour of a "new cooperation with homosexuals in society" and officially meeting the Association for Gays and Lesbians for talks.

Woelki said the archdiocese's finances had "stabilized and improved" thanks to "courageous and responsible decisions" and "great sacrifices" by church institutions.

He added that the archdiocese was forecast to lose a further third of its membership by 2030, and he said Catholic schools, nurseries, hospitals, elderly homes and information centers would also be reorganised to reflect this shift.

[15] The announcement followed the completion of a complicated process that governs the determination of a new archbishop of Cologne and which requires several levels of ecclesiastical and civil review.

Following Meisner's retirement, the archdiocesan cathedral chapter, which consists of the leading priests of the archdiocese, composed a list of candidates, which was passed to the pope via the papal nuncio in Berlin.

According to the terms of the concordat governing Catholic ecclesiastical affairs in the state of North Rhine-Westphalia, the regional parliament must certify that the newly nominated archbishop poses "no concerns of a political nature".

[16] In October 2016 he was appointed a member of the Congregation for Divine Worship and the Discipline of the Sacraments by Pope Francis for a five-year renewable term.

[17] The proposal to expand Holy Communion was rejected on 25 May by Cardinal-elect Luis Ladaria Ferrer, Prefect of the Congregation for the Doctrine of the Faith, who said that there were "a series of problems of considerable importance".

He continued: All those inside and outside the Church who so vehemently push for changes (liberalizing celibacy, reconsidering homosexuality, ordaining women, accepting sex outside of marriage) have not answered one question: Why are Protestant Christians in Germany not flourishing?

Does that not indicate that the real problems lie elsewhere, and that the whole of Christianity has to confront a crisis of faith and understanding, rather than adapt to a "new reality of life" that is presented as irresistible?

Woelki decided in 2015 not to notify Rome of this case because of the "bad health of the priest" involved and because the "victim refused to offer testimony".

[22] Johannes-Wilhelm Rörig, appointed by the Federal Ministry of Family Affairs, Senior Citizens, Women and Youth to fight child abuse, made the criticism in 2020 that the Roman Catholic Archdiocese of Cologne led by Woelki was the only one that was not making progress.

[23] Rörig criticised Woelki for ordering a report on the handling of sexual abuse cases in the Archdiocese of Cologne but refusing to make it public when it was finished.

[29] After a review of the situation surrounding the reports, the Vatican concluded in June 2021 that Woelki had made "grave errors" but said no evidence had been found that his actions were criminal under secular law.