He authored around thirty novels and numerous popular science articles, blending scientific exploration with adventure narratives aimed at educating young readers, which is why much of his fiction is classed as young-adult literature.

Umiński’s novels popularized concepts like aviation and space exploration in Polish literature, while his journalism spanned science, education, and literary criticism.

Despite waning popularity posthumously, his contributions to Polish literature and education earned him accolades, including the Officer's Cross of the Order of Polonia Restituta in 1952.

At 15 he wrote his first fiction, the short story "Z Korsyki" ("From Corsica"), and published it in the magazine Przyjaciel Dzieci [pl] (The Children's Friend).

[3]: 436 [5][6][a] After obligatory service in the Imperial Russian Army (as a sapper), he studied in the Department of Natural Sciences at Saint Petersburg University.

[8]: 328 [6][3]: 436 [9] After World War I he reduced his journalistic activities, although in 1933 he wrote some content for the aviation magazine Lot Polski [pl].

[3]: 436 In 1891 he published his first novel Zwycięzcy oceanu (Conquerors of the Ocean), which received a number of editions since (as well as a translation to Czech).

[9] In 1921 he published a 15 volume set of his collected works in the series Wybór powieści dla młodzieży (Selection of Novels for the Youth).

His 1911 novel Samolotem naokoło świata, and possibly some earlier works, popularized the modern Polish word for the airplane (samolot), which he is sometimes credited with coining in that context.

[6] After Poland regained independence, he worked for several government institututions (Emigration Department in 1918; press representative for the Ministry of Internal Affairs, in 1921, later, Film Office).

[3]: 436  He was a member of the Professional Association of the Polish Writers [pl] (Związek Zawodowy Literatów Polskich, ZZLP).

[6] His final novel, science fiction story Zaziemskie światy (Otherworldly Worlds), finished during wartime, was held by censors who cancelled the initial print in 1948, it was published posthumously in 1956.

[5] He left an unfinished novel manuscript, Świat za lat tysiąc (The World in a Thousand Years), which was likely inspired by Wells' The Time Machine.

[16]: lxv  Another novel finished near the end of his life, O własnych siłach (about wartime orphans), and its sequel, were never published and are now considered lost.

The books are optimistic; Niewiadomski and Smuszkiewicz write further that "In the clash with nature, civilization achieves an unquestionable victory", and the characters grow through adversity.

[11]: 205 From modern perspective, his works have been criticized for not delving into societal issues or transformation of future society, and his science fiction ideas have been noted to have been not particularly revolutionary or imaginative, rather, simple extrapolations and improvements of existing technologies (gramophones, submarines, aircraft).

[18]: 44 [11]: 205  Polish literary scholar Kamila Budrowska [pl] suggested that his science fiction themes should be seen more through the prism of his educational activities than experiments with imagination.

[19]: 116 [20]: 61 Umiński's positive view of technological progress changes in his late works (Zaziemskie światy) which likely reflect his wartime disappointment at the destructive consequences of said trend.

[7]: 586  Likewise, Niewiadomski and Smuszkiewicz note that despite the increasing obsolescence of the science-fictionish gadgets featured in his works, the stories themselves benefit from "a compact, interestingly constructed plot modeled on the adventurous novels of Thomas Mayne Reid and Robert Louis Stevenson, a simple narrative, and not too obtrusive didacticism, so they are still well-deservedly popular with readers.