debut novel; first novel
Refers to an author's first published novel. Often used in literary contexts.
Her debut novel won a major award.
処女作 is a broader term for a debut work in any creative field, while 処女小説 specifically refers to a debut novel.
Compound of 処女 (shojo, 'virgin; maiden') and 小説 (shōsetsu, 'novel'), literally 'maiden novel', referring to an author's first novel.