In his seventeenth year, having acquired a knowledge of shorthand, he joined as a reporter the staff of The Munster News, a bi-weekly paper published in Limerick.
At the same time he began to contribute verse to The Nation, the organ of the Young Ireland party, and continued to write prose and poetry for it until his death, twenty years later.
Charles Dickens, who then edited the latter journal, wrote the young poet an encouraging letter, and showed kindly interest in him.
He also acted as London correspondent of The Irish People, the organ of the Fenian movement, which, with John O'Leary as its editor, was founded in November 1863, and was suppressed by the government in September 1865.
Under the auspices of the Southwark Irish Literary Society, O'Donnell's poems were published in 1891, and his grave was marked by a Celtic cross.