CCR4-associated factor 1 (CAF1) plays an important regulatory role in the stress response of plants. However, no study has evaluated the CAF1 regulation of the stress response in poplar. In this study, 19 PtCAF1 genes were identified in the genome of Populus trichocarpa. A phylogenetic analysis of the PtCAF1 gene family in Arabidopsis thaliana and Oryza sativa was carried out to investigate the evolution of PtCAF1. The full-length CDSs of 16 PtCAF1 were cloned from P. trichocarpa, and PtCAF1Q was identified based on the expression levels of PtCAF1 genes from poplar by the drought treatment. Sequence alignment revealed that PtCAF1Q contained three motifs and was highly similar to the sequences of CAF1s of other species. The expression pattern of PtCAF1Q was similar in Nanlin895 (Populus deltoides × P. Sudamericana) and Shanxinyang (Populus davidiana × P. bolleana Loucne). In addition, PtCAF1Q was responsive to abscisic acid (ABA), MeJA, SA, NaCl, PEG6000, H2O2, and cold stresses. Transgenic poplars were generated using Agrobacterium tumefaciens infection. RNA-sequencing showed that differentially expressed genes (DEGs) were linked to plant hormone signal transduction, the MAPK signaling pathway, biosynthesis of secondary metabolites, carotenoid biosynthesis, and other pathways, most of which were located in the ABA signaling pathway. Under drought stress, PYL and SnRK2 in the ABA pathway were significantly upregulated, PP2C was significantly downregulated, and downstream transcription factors and stress-resistant genes were significantly upregulated. The proline contents and peroxidase and superoxide dismutase activities of transgenic plants were increased, whereas the malondialdehyde level was significantly decreased. PtCAF1Q overexpression upregulated PYL and SnRK2 in the ABA pathway by downregulating PP2C and increased the expression of stress-related genes and transcription factors. Also, the activity of antioxidant enzyme was improved and drought resistance of poplar was enhanced. Overall, these results reveal that PtCAF1 plays an essential role in drought-stress resistance through the regulation of the stress response in poplars.