Brantz Mayer was a prominent nineteenth-century Baltimore citizen, historian, and writer. He was born to Christian Mayer (1763-1842) and Anna Kat(h)erina (Baum) Mayer (1767-1843) in Baltimore, Maryland, on September 27, 1809, the youngest of ten children. His father came to the United States from Ulm, Wörttemberg, Germany, and settled in Maryland in 1784. After emigrating to the United States, Christian Mayer established himself as a trader. Later he became the president of a Baltimore insurance company. Eventually, he served as the consul-general of Wörttemberg to the United States.
Brantz Mayer attended public school, as well as St. Mary's Seminary in Baltimore but was primarily privately educated. He completed his study of law at the University of Maryland and was admitted to the bar in 1832. Throughout this period, he traveled extensively throughout the United States, Asia, and Europe. On September 27, 1835, Mayer married Mary Griswold (1817-1845). Before her death in 1845, Mary bore five daughters: Katherine Mary (Kate) (b. 1836), Beata (b. 1838), Anna Maria (b. 1841), Dora (b. 1844-1878), and Mary (b. 1845). On November 15, 1848, the widower married Cornelia Poor (b. 1818), with whom he had three daughters: Cornelia (Nellie) (b. 1849), Jane (b. 1851), and Fanny (b. and d. 1854).
Mayer left the practice of law in 1841 to take a position as the secretary of the United States legation in Mexico. Following his return from Mexico in 1844, Mayer began his life-long study of, devotion to, and preservation of history, especially local history. He was involved in the establishment of the Maryland Historical Society in 1844 and served as its president from 1867 to 1871. Additionally, he served as president of the Library Company of Baltimore and proved vital in the construction of the Athenaeum Building in the city. He later encouraged the state of Maryland to establish an archives commission and depository, which was ultimately housed at the Historical Society.
In 1844, Mayer published the first of many historical works, Mexico as It Was and as It Is. This first work was of particular importance, given the pending Mexican-American War. Other works by Mayer include Tah-Gah-Jute: or Logan and Captain Michael Cresap (1851), Mexico, Aztec, Spanish and Republican (1851), and Calvert and Penn (1852). He also edited several works, including the Journal of Charles Carroll of Carrollton, during His Visit to Canada in 1776 (1845) for the Maryland Historical Society, and Captain Canot; or Twenty Years of an African Slaver (1854). He continued to write and to publish until shortly before his death. In addition to books, Mayer regularly wrote editorials and columns for newspapers in the Baltimore area, especially the Baltimore News American.
During the Civil War, Mayer served as a brigadier-general with the Maryland volunteers and he assisted in recruiting for the state. In 1863, he received the post of additional paymaster. In January 1865, he was promoted to major and paymaster in the United States regular army. In 1866, he was promoted again, this time to lieutenant-colonel (retroactive to November 1865) for his service during the war. Mayer retired from the pay department in 1875 at the rank of colonel. He died on February 23, 1879 at the age of sixty-nine.