[2][3] He studied at the Ludwig-Maximilians University in Munich in 1963, he earned a doctorate in history (doctoral thesis: "Das Wiedererstehen katholischer Gemeinden in den Fürstentümern Ansbach und Bayreuth", 'The reestablishment of Catholic parishes in the principalities of Ansbach and Bayreuth'); and he obtained the "habilitation" in 1967 with the dissertation "Das Konzil von Pavia-Siena (1423–1424)" ('The council of Pavia-Siena').

A specialist in the history of the councils, he is founder and editor of the journal Annuarium conciliorum historiae (Paderborn, 1969); and of the series "Konziliengeschichte" (1979), which has published 37 volumes so far.

On 20 November 2010 Pope Benedict XVI elevated Brandmüller to the College of Cardinals as Cardinal-Deacon of S. Giuliano dei Fiamminghi.

The first dubium concerned the reception of the sacraments by the divorced and remarried; the other four asked about fundamental issues of the Christian life, and referenced Pope John Paul II's encyclical Veritatis splendor.

In November 2016, having not received a response, they publicised their letter, entitled "Seeking Clarity: A Plea to Untie the Knots in Amoris Laetitia".

[6][7] In May 2017, Caffarra, Brandmüller, Burke and Meisner sent a private letter dated 25 April and hand-delivered to the Pope on 6 May asking for an audience, having received no response to the dubia they had earlier sent him in September 2016.

[9] In February 2019, Brandmüller and Burke penned an open letter addressed to Pope Francis calling for an end of "the plague of the homosexual agenda", which they blamed for the sexual abuse crisis engulfing the Catholic Church.