Baker first studied law in the office of his brother, later Governor, Thomas Johnson, at Annapolis, afterwards settling in Frederick County in 1776 to engage in the practice of that profession. During the Revolution he commanded a battalion with the rank of Colonel in the brigade of his brother Colonel James Johnson and fought at the 1777 Battle of Paoli, near what is now Malvern, PA. Following the Revolution, he became a leading member of the bar of Frederick and of the General Court.

As with others of the Johnson family who died in Frederick County, Baker was reinterred in Mt. Olivet sometime after its creation in 1854. His original burial location is now unknown, but likely in one of the church graveyards in then Fredericktown, as was his brother Joshua, or perhaps in a family burial ground on Johnson property, as was his brother Roger. Many of the church burial grounds in town were sold and the land built upon afterwards and most of the Johnson properties later sold and passed out of the family. Of those reinterred from those locations to Mt. Olivet, including some Johnsons, not all today have replacement markers, their locations unknown.

Note: The noted exact dates of birth and death are per Colonial Families of the United States and thought correct.

From the Newspaper Abstracts of Frederick County 1811-1815, citing the Fredericktown Herald of June 22, 1811:
"Died Tues morning last, Col. Baker JOHNSON of this town, who during 15 months of severe indisposition preceding his death, suffered every poignant extreme of excruciating pain; he was a native of Calvert Co., but immigrated early in life to Frederick, where he entered into the profession of the law. He marched at the head of his regiment during Rev. War, then resumed his vocation at the Bar."

From the Federal Gazette (Baltimore) of June 26, 1811:
"DIED, at Frederick-town, the 16th insant (sic), Col Baker Johnson, another patriot of the revolution which established the Independence of the United States. Orthodox in the principles of the Federal constitution, he animated the wavering, and overawed the disaffected. - Hospitably polite, his house was open to his numerous friends passing thro' the town, who always felt at home. He has left a numerous family to lament his death, and to imitate his numerous virtues."