After an early education in private schools and under tutors, he graduated from Williams College with the degrees of Bachelor and Master of Arts, and Doctor of Civil Law. In 1872 he became connected with the New York Evening Post, which his father owned in partnership with William Cullen Bryant and John Bigelow, became assistant publisher in 1875, and from 1877 was publisher, stockholder, and member of the Board of Trustees.

Selling his interest in the Evening Post in 1881, he went to Europe and lived in London and Rome. In 1896 he became a Roman Catholic, adopting the name of Austin at his Confirmation. In 1903 he was appointed private chamberlain to Pope Pius X.

In 1886 Henderson published his first novel, The Prelate, and followed it two years later with Agatha Page. The latter, soon (1892) dramatized as The Silent Battle, was produced by Sir Charles Wyndham at the Criterion Theatre, London, another dramatic version, entitled Agatha, being produced the same year at the Boston Museum. His second drama, The Mummy and the Humming Bird, was presented at Wyndham's Theatre, 1901, the principal male part being again taken by Wyndham. In 1902 it was played at the Empire Theatre, New York.