At the age of eight, Hosmer's desire to act was stimulated by witnessing a performance of Douglas Jerrold's play Black-Eyed Susan.

[4] She attended the Genesee and Wyoming Seminary in Alexander, New York, for a short time but remained committed to having a career on the stage.

[5][2][6] At the age of 16, under the tutelage of actor Barton Hill, she gained her first speaking role at the Metropolitan Theatre and was soon promoted to member of the theater's stock company.

[5] In 1860, while a leading actress, the young Hosmer was noticed by McVicker's Theater in Chicago and was recruited by the playhouse for its company.

She came among us unheralded and unpuffed; content, it would seem, to rely on her own intrinsic merits, and stand or fall by the freely-expressed opinion of her auditors and the critical acumen of the press.

This was noted by English theater critic Clement Scott during an 1878 production of Lucrezia Borgia:There were moments when I felt almost paralyzed by her acting.

[3][1] In the winter of 1889–90, Hosmer took a job acting with the small Ramage's Standard Theatre company playing in Midwestern towns.

He better represented the genius of his father, the first Junius Brutus Booth, and he played with such fire and vigor that he made us in his company actually fear him.