In May 1982, he was appointed Bishop of Evreux.
A man of practical experience, Jacques Gaillot has often commented the every day events. In 1983 he publicly supported a young conscientious objector on trial at the Evreux Court. In October 1983, at the Annual Conference of the French Bishops, he was one of the two Bishops to vote against the text on nuclear deterrence.

In 1985 he supported the Palestinian uprising in occupied territories and met with Yasser Arafat in Tunis. He was invited to attend the Organization of the United Nations for an extraordinary session about nuclear disarmament.

In July 1987, he went to South Africa to meet a young activist against apartheid from Evreux who was condemned by the Pretoria Administration to a four-year jail sentence. To be able to travel there he had to cancel his attendance to a diocese pilgrimage to Lourdes. He was bitterly criticized for that.

In the plenary assembly in camera of the French Bishops in Lourdes in November 1988 he proposed married men the right to become priests.
In October 1989, he participated in French Polynesia to a demonstration organized by the Movement for Peace for stopping the French nuclear assays.
On December 12, 1989, he was the only French Bishop to attend to the ceremony of ashes transfer to the Pantheon in Paris of Abbey Gregoire. (Abbey Gregoire was a member of the National Assembly during the French revolution in 1789. Among many humanitarian actions he made adopted the abolition of slavery and obtained the civil and political rights for the Jews, he was one of the minority of the French clergy to declare his fidelity to the Republic. Note of the translator.)

He made known in 1991 his opposition to the Golf war by writing a book entitled «Open letter to those who preach war and have it done by others» He also condemned the blockade of Iraq.

Jacques Gaillot organized a three-year synod in his diocese. He wrote a dozen books, one became a best seller with the title «A cry of anger against exclusion». In this book he severely criticized the laws against immigration supported by the Minister of Interior at that time. This was one reason used by Rome for his dismissal.

In all these interventions, Jacques Gaillot is convinced that the media should be used to communicate with the modern world. He has a free speech and does not dare to use «I», he wants to be clear and simple in his statements.
Some of the major characteristic features of his fidelity to the Gospel are the care for the poor and the fringes of society, the refusal of any accommodation, and an attachment to right, justice and peace. He is convinced that Jesus belongs to humanity, not only to the Christians. The search for the lost sheep is worth letting the others into the flock.

In 1995, Jacques Gaillot was called to go to Rome. The verdict was given. «Tomorrow, on Friday January the 13th at 12 o'clock, you will cease to be Bishop of Evreux» Jacques Gaillot was given the title of Bishop of Partenia, a seat on the High lands of Setif in Algeria, where he did his military service. The seat of Partenia disappeared in the fifth century, now it has become the symbol of those who, in the Church or in the Society, have the feeling of never existing.
The Rome decision was misunderstood by many in France and abroad, it left a feeling of unfairness among Christians and non-Christians.

Leaving his seat of Evreux, Jacques Gaillot established his lodging for a year in the famous squat, Dragon Street in Paris, among families of immigrants of which their legal permit was cancelled by the new law. Belonging to various associations defending the rights of these immigrants and those having no lodging, he became the Bishops of the poor and excluded. Often he was asked to defend political prisoners and human right activists abroad.

In 1995, he published the book « Je prends la liberté (I choose liberty) » at Flammarion , Ed.

In 1996, the Partenia web site was created. Very rapidly this site was operated from Zurich and became accessible in 7 languages with a forum, a logbook, a series of comments on the Bible and interventions on every day issues.
The Spiritan community in Paris welcomed Jacques Gaillot and he usually resides there. Till a few months ago he was having his office in the «Maison des Ensembles» a squat in Paris of immigrants without legal permit, but the police expelled them and his office.

On May 2000, the President of the Conference of the Bishops of France on the occasion of the Jubilee took the initiative to invite him to an ecumenical meeting in Lyon. He sent him a letter that became public later on: «It is important that Catholics and, more so the public opinion know that the communion that unites us like brothers is real, even though it is lived in a particular manner».
He closed his letter in writing: «you do remain our brother in the episcopate».
This bright spell was not followed afterwards.

In 2003, he published « A Catechism with a taste of freedom » in collaboration with Alice Gombault and Pierre de Locht .