Tanner was born in Pittsburgh, Pennsylvania, the first of seven children.
His middle name commemorated the struggle at Osawatomie between pro- and anti-slavery partisans.
His father Benjamin Tucker Tanner (1835-1923) was a bishop in the African Methodist Episcopal Church, the first independent black denomination in the United States.
Being educated at Avery College and Western Theological Seminary in Pittsburgh, he developed a literary career.
In addition, he was a political activist.
His mother Sarah Tanner was born into slavery in Virginia but had escaped to the North via the Underground Railroad.
She was mixed race, and Tanner himself was either a quadroon or an octoroon.
The family moved to Philadelphia when Tanner was young. There his father became a friend of Frederick Douglass, sometimes supporting him, sometimes criticizing.
Tanner is often regarded as a realist painter, focusing on accurate depictions of subjects.
While works such as The Banjo Lesson were concerned with everyday life as an African American, Tanner later painted themes based on religious subjects, for which he is now best known.
It is likely that Tanner's father, a minister in the African Methodist Episcopal Church, was a formative influence for him.
Tanner's body of work is not limited to one specific approach to painting and drawing.
His works vary from meticulous attention to detail in some paintings to loose, expressive brushstrokes in others.
Often both methods are employed simultaneously.
The combination of these two techniques makes for a masterful balance of skillful precision and powerful expression.
Tanner was also interested in the effects that color could have in a painting.
Many of his paintings accentuate a specific area of the color spectrum.
Warmer compositions such as The Resurrection of Lazarus (1896) and The Annunciation (1898) express the intensity and fire of religious moments, and the elation of transcendence between the divine and humanity.
Other paintings emphasize cooler, blue hues.
Works such as The Good Shepherd (1903) and Return of the Holy Women (1904) evoke a feeling of somber religiosity and introspection.
Tanner often experimented with light in a composition.
The source and intensity of light and shadow in his paintings create a physical, almost tangible space and atmosphere while adding emotion and mood to the environment.
Tanner also used light to add symbolic meaning to his paintings.
In The Annunciation (1898) the angel Gabriel is represented as a column of light that forms, together with the shelf in the upper left corner, a cross.
This view of the representation of Gabriel is consistent with James Romaine's comment that "Through the visual language of her pose and expression Tanner draws the viewer into Mary's inner life of virtue, trepidation, acceptance, and wonderment."
Mary's acceptance includes her acceptance of the cross that she will have to bear by consenting to be the Lord's handmaid (Luke 1:38).