Modern drug discovery programs utilize a wide variety of technologies to aid in identification of potential drug targets, and progress them through the often long and winding path of finding novel drug-like molecules. Recombinant cell-based assays are an important tool in the drug discovery process for investigating the biological mechanisms of potential drug targets and conducting screening campaigns in the hunt for biologically active molecules. Historically, stable cell lines expressing the target protein(s) of interest have been used for these assays. Although such cell lines can be useful, their development can be laborious and the resulting cell line affords little experimental flexibility. Transient gene expression approaches provide an alternative to the often tedious task of developing and maintaining numerous stable cell lines. Recently the unique properties of modified baculoviruses, containing mammalian expression cassettes and referred to as BacMam viruses, have been exploited to facilitate rapid and reproducible transient cell-based assay development. This review will focus on the many features of BacMam virus gene delivery that make it a powerful system for cell-based assay development and screening.