[2] After 1989, he was often presented as a political opportunist during his mature years lived in communist Poland, where he held high offices (participated in the slander of Polish expatriates, literary and other figures who after World War II remained in the West).

In 1914, he travelled in Sicily and North Africa with his friend and distant cousin Karol Szymanowski, a composer for whose opera King Roger he later provided the libretto.

[6] After World War I, in October 1918 Iwaszkiewicz came to Warsaw, where he joined a group of young artists associated with the Pro Arte et Studio magazine.

He was secretary to the Society for the Encouragement of Fine Arts (Towarzystwo Zachęty Sztuk Pięknych) and from 1925 a member of the Polish PEN Club.

[1] From 1927 with the Foreign Ministry, first appointed the head of the art promotion section of the Press Department and later sent as secretary of the Polish mission to Copenhagen (1932–1935) and Brussels (1935–1936).

[1] During World War II, Iwaszkiewicz participated in the Polish Underground State's activities, working in the Department of Education, Science and Culture of the Government Delegation for Poland.

Iwaszkiewicz and his wife Anna had extensive contacts within the Jewish-Polish intelligentsia circles and assisted their former neighbors, friends and acquaintances in a variety of ways during the German occupation of Poland.

Iwaszkiewicz family's Villa Stawisko residence served as a hiding place for many Jews and Poles who faced the threat of being arrested by Nazi Germans, especially after the fall of the Warsaw Uprising in 1944.

Iwaszkiewicz wrote of his deeply socialist convictions, but was ambivalent and privately bitter about the political reality of the Polish People's Republic, within which he officially functioned.

[3] Iwaszkiewicz wrote novels and short stories, poems, dramatic works, essays and columns, and translations from French, English, Russian and Danish literatures.

He wrote plays based on classical motifs and many miscellaneous pieces reflecting his interests and pursuits in areas such as music and theatre, travel, and popularization of culture.

He concluded, "One is almost inclined to believe that some people are gripped by circumstances meant for them, and that for him the good fortunes, after his impoverished youth, began in the interwar period, to endure also later".

Iwaszkiewicz experienced and described a particularly intense relationship with a younger man terminally ill with tuberculosis; it commenced when the writer was over sixty years old.