Genetically encoded effectors are important tools for probing cellular function in living animals, but improved methods for directing their expression to specific cell types are required. Here, we introduce a simple, versatile method for achieving cell-type-specific expression of transgenes that leverages the untapped potential of “coding introns” (i.e., introns between coding exons). Our method couples the expression of a transgene to that of a native gene expressed in the cells of interest using intronically inserted “plug-and-play” cassettes (called “Trojan exons”) that carry a splice acceptor site followed by the coding sequences of T2A peptide and an effector transgene. We demonstrate the efficacy of this approach in Drosophila using lines containing suitable MiMIC (Minos-mediated integration cassette) transposons and a palette of Trojan exons capable of expressing a range of commonly used transcription factors. We also introduce an exchangeable, MiMIC-like Trojan exon construct that can be targeted to coding introns using the Crispr/Cas system. Display omitted •Plug-and-play reagents for gene- and cell-type-specific transgene expression in vivo•Binary and intersectional targeting is enabled for multiple transcriptional factors•Trojan exons couple to “off-the-shelf” Drosophila stocks bearing intronic MiMIC transposons•T-GEM Trojan exon can be used with the Crispr/Cas system to target introns in arbitrary genes of interest Genetic manipulation and monitoring of cellular function in living animals requires tools for targeting transgene expression to specific cell types. Diao et al. present a “Trojan exon” approach that removes a common bottleneck in transgene targeting by facilitating the rapid production of transgenic organisms that can express transcriptional effectors in targeted cell types. The method uses off-the-shelf components in Drosophila and is modular, simple, fast, and precise.