Miller was born free early in the 1840s, probably in the western part of Henrico County and was the son of John Miller, a cooper, and Susan Miller, in whose household he resided at the time of the 1860 U.S. Census, which identified him as a barber. Election and legislative records identify him as J.B. Miller Jr., but other sources also refer to him as John Miller Jr. In 1859 his father deeded him a piece of property in the area of Henrico County that was later located on Belvidere Street in the city of Richmond. It is not known when or where he learned to read and write nor is it known what he did during the American Civil War (1861-1865) or immediately afterward. He was probably living in Richmond in May 1867, when he was named to the jury pool of the United States Circuit Court and would have been part of the interracial jury for the trial of former Confederate president Jefferson Davis had it been held. In 1870 Miller was teaching school in neighboring Goochland County, where his mother had been born. By then, he was married to Francis, surname unrecorded, and had one young daughter and two young sons. During the following decade they had another son and another daughter.
It is unclear when and how Miller became involved in Republican Party politics in Goochland County. In June 1869 he received the party’s nomination for the House of Delegates. On July 6, when voters ratified the state’s new constitution, they also elected state officers and members of both houses of the General Assembly. On that day, Miller defeated a white 1,394 to 825 to represent Goochland County for a two-year term in the House of Delegates. The white Conservative Speaker of the House appointed Miller, one of the first African American legislators in Virginia history, to the lowest-ranking seat on the relatively inconsequential Committee on Officers and Offices at the Capitol.
At the short special session of the General Assembly in October 1869, Miller voted to ratify the Fourteenth and Fifteenth Amendments, which Congress required before it seated senators and representatives from Virginia. Miller was clearly interested in protecting the rights and interests of African Americans. He attempted without success to have the House invite African American ministers to open sessions with prayers, and he introduced a proposal to establish a maximum ten-hour day for farm laborers with a minimum wage of $1.00 a day and $0.25 per hour for every extra hour. It did not pass nor did his proposal to prohibit conductors on railroads from discriminating on the basis of color. The terms of a bill Miller introduced respecting county property are not known, but it evidently did not pass, either. On June 29, 1870, when members debated the bill to establish the state’s first free public school system for all children, Miller moved to strike out the requirement for racial segregation of students. It failed 19 to 80. He and most of the other African American delegates then voted against the bill that they favored as their only means of protesting the imposition of racial discrimination.
Miller reintroduced a similar version of his 1870 antidiscrimination bill in the 1870–1871 session of the General Assembly. He then proposed that “any captain, conductor, or agent of any public conveyance of this State that should make any distinction on account of color, shall be fined not less than $300, nor more than $500, and imprisoned for not more than five years nor less than three years.” The motion died in committee. In March, near the end of that session, Miller joined most of the other African American legislators in voting for a bill to refinance the pre–Civil War public debt. The measure seemed prudent at the time to preserve the state’s credit, but it led to more than a decade of political turmoil because paying interest on the debt required severe reductions in appropriations for the public schools.
Miller took part in an attempt in March 1870 to unite the state’s divided Republican Party, but he did not receive the party’s nomination for a second term in the House of Delegates in the autumn of 1871. Goochland County’s Republicans were evidently also divided, and, an African American, eventually replaced the white man who had originally been nominated for the House of Delegates. In April 1873 Miller was elected chairman of the Goochland Republicans. He returned to Richmond and at some point resumed his original profession of barber. He may have suffered some financial difficulties. He and his wife mortgaged his Richmond property in 1871 and his father was forced to purchase it when it was auctioned in March 1875 for non-payment of the debt. In the autumn of 1875 Miller was charged with a felony for fraudulently obtaining a signature on a financial note but was acquitted. John B. Miller Jr. continued to appear in Richmond’s city directories until 1885, but the time and place of his death are unknown, although a February 1896 newspaper article on members of the 1867 interracial jury described him as “now dead.”