The parishes are grouped into 13 deaneries for administrative purposes: Bay Area, Bluebonnet, Central, Eastern, Galveston Mainland, Northeast, Northern, Northwest, San Jacinto, Southeast, Southern, Southwest, Western.

Odin opened several schools and invited the Ursuline nuns as the first religious community in Texas to operate them.

[12] He also visited remote parts of Texas, and twice traveled to Europe to recruit priests and obtain material help for the diocese.

[15] After the end of the American Civil War in 1865, Dubuis established additional parishes, hospitals and schools in the Diocese.

On one trip to Europe, he secured the services of the Congregation of the Resurrection to minister to the Polish community in Texas.

[18] Dubuis founded the Sisters of Charity of the Incarnate Word, which played a significant role in healthcare services in Texas.

[19][20] In 1873, the Sisters of Notre Dame de Namur established the Academy of the Sacred Heart for girls in Waco.

For the next ten years, in an unusual arrangement, Gallagher served as apostolic administrator in Galveston without a diocesan bishop.

[23] He established St. Mary's Seminary at La Porte in 1901, and Good Shepherd Home for Delinquent Girls at Houston in 1914.

Pope Benedict XV named Christopher Byrne from the Archdiocese of Saint Louis as the fourth bishop of Galveston in 1918.

[26] In 1936, Byrne helped organize the centennial celebration of Texan independence from Mexico, holding an open-air mass at the San Jacinto Battlefield near Houston.

That same year, Pope Pius XII named Wendelin Joseph Nold of Dallas coadjutor bishop in Galveston to assist Byrne.

[34] In 1979, Pope John Paul II elevated the status of St. Mary Cathedral to that of a minor basilica.

In 2004, John Paul II created the new Ecclesiastical Province of Galveston–Houston and elevated the Diocese of Galveston–Houston to the Archdiocese of Galveston-Houston.

[35] Two years later, Pope Benedict XVI named Bishop Daniel DiNardo from the Diocese of Sioux city as a coadjutor archbishop in Galveston-Houston to assist Fiorenza.

[5] In 2002, then Bishop Fiorenza issued a statement that the diocese would "make the protection and safety of children and young people a top priority".

[38] A 2006 news report by the Houston Press said that Fiorenza had a tendency to accept troubled clergy into the archdiocese.

The article also stated that the archdiocese frequently acted to protect itself from public scrutiny, mounting vigorous legal defenses to lawsuits, blaming the victims for their abuse, and obfuscating for the news media.

[39] On January 30, 2019, Archbishop DiNardo released a list of names of 40 priests from the archdiocese with credible allegations of sexual misconduct over the previous 70 years.

DiNardo was criticized for allowing Keller to offer mass publicly at his parish the morning after the list was released.

[41] In December 2020, Manuel La Rosa-Lopez pleaded guilty to two counts of indecency with a child and was sentenced to 10 years in state prison.

The crimes took place at Sacred Heart Catholic Church in Conroe between 1997 and 2001; the victims were an underage boy and girl.

[43] The archdiocese was sued for $10 million in 2021 by the parents of a girl they said was sexually abused by Phi Nguyen, an archdiocesan priest.

Nguyen had allegedly touched the girl inappropriately during a mock confession at Nazareth Academy in Victoria in 2018.