Since 1925 published short stories and feuilletons in periodicals. The first short story "Lelia's Dream" appeared in the youth magazine "Ateitis" (1926, No. 4). Signed under the pseudonym Juozas Kriaušė. For several months he edited the Catholic youth magazine "Pavasaris". Here he published short stories, signing under the same pseudonym: Juozas Kriaušė is a Lithuanianized Gruš. He signed the pamphlets under the pseudonym of Liongins Padanginė. The first collection of short stories "Ponia Bertulienė" was published in 1928, and the most popular of the prose works was the novel "Karjeristai" (1935).
Since the 20th century In the 1950s, J. Grušas became the most productive Lithuanian playwright. The creator legitimized the genres of tragedy (historical drama "Herkus Mantas") and tragicomedy (drama "Love, Jazz and the Devil") in Lithuanian dramaturgy. He created a theater of moral judgment and a unique type of drama that combines traditional and modern drama trends. Many works of J. Gruš have been staged in the Kaunas Drama Theater. "Barbora Radvilaitė" (1972) was recognized as the performance of the century. 1980-1981 five volumes of J. Gruš's "Writings" were published. in 1992 based on the play "Love, Jazz and the Devil", the feature film "Jazz" (dir. Raimundas Banionis) was created.
