The life history and immature stages of development of the wasp Trichopria drosophilae (Hymenoptera: Diapriidae), a biocontrol agent of drosophilid flies (Diptera: Drosophilidae), including the invasive Drosophila suzukii, were investigated. T. drosophilae develops as a solitary endoparasitoid from egg to adult in 22–26 days under laboratory conditions at room temperature. The egg of T. drosophilae is broad ovate, with a short petiole when freshly laid and is subsequently getting more elongate. There are three larval instars in T. drosophilae. The freshly hatched first instar larva has a narrow caudal part with a bifurcated indentated abdominal appendage, enlarged thoracic egments and a head with sclerotized sharp mandibles and large labial palpi. The second instar is poorly sclerotized with peculiar everted (exodont) mandibles. The third instar is grub-like, with three pairs of thoracic spiracles and stylet-shaped mandibles. The pupa of T. drosophilae is semitransparent and surrounded by numerous meconium pellets within the host puparium. Competition between conspecific rivals is observed. The siblicide is conducted using both the sharp mandibles and the small labrum and labium, which function like a sucker enabling emptying the rival's body. In the case of superparasitism, the first-instar larvae of the parasitoid are encapsulated within serosa membranes. Also, the peculiarities of adult morphology of T. drosophilae, as well as a comparison to similar European Trichopria species, are provided.