He was a member of the Rhymers' Club, which included W. B. Yeats and Lionel Johnson. He was also a frequent contributor to the literary magazines The Yellow Book and The Savoy. Dowson collaborated on two unsuccessful novels with Arthur Moore, worked on a novel of his own, Madame de Viole, and wrote reviews for The Critic.
Dowson was also a prolific translator of French fiction, including novels by Balzac and the Goncourt brothers, and Les Liaisons dangereuses by Choderlos de Laclos.
In 1889, at the age of 23, Dowson fell in love with the eleven-year-old Adelaide "Missie" Foltinowicz, the daughter of a Polish restaurant owner. Adelaide is reputed to be the subject of one his best-known poems, Non Sum Qualis eram Bonae Sub Regno Cynarae. He pursued her unsuccessfully, and in 1897 Dowson was crushed when she married a tailor who lodged above her father's restaurant.
In August 1894 Dowson's father, who was in the advanced stages of tuberculosis, died of an overdose of chloral hydrate. His mother, who was also consumptive, hanged herself in February 1895, and soon Dowson began to decline rapidly.
Robert Sherard found Dowson almost penniless in a wine bar and took him back to the cottage in Catford where he was himself living. Dowson spent the last six weeks of his life at Sherard's cottage and died there of alcoholism at the age of 32.