Flowering time, maturity, and plant morphology have considerable effects on the adaptation and grain yield of soybean (Glycine max). The identification of novel genes and an understanding of their molecular basis are critical to improve soybean productivity. In this study, we cloned a flowering time related APETALA2-like gene GmTOE4a and generated GmTOE4a-overexpressing lines in the cultivar Williams 82. The transgenic lines exhibited late flowering both under long day and short day conditions, and repressed the flowering-related genes, including GmFT2a, GmFT5a, GmAP1, and GmLFY, whereas the flowering repressors GmFT4 and miR156 were upregulated. Interestingly, GmTOE4a was also mediated by photoperiod via maturity genes E3 and E4, which encode photoreceptors in soybean. Further, miR172-mediated GmTOE4a, which regulates flowering in soybean, is different in Arabidopsis in that it is dependent on the CONSTANS-like gene GmCOL1a. In addition to its effect on flowering time, GmTOE4a regulated plant morphology, increased stem thickness, and reduced plant height, internode length and leaf size, which are important agronomic traits that enhance the capacity to resist lodging and increase soybean yield. This is useful information to understand the molecular mechanism of flowering time and plant morphology in soybean and will greatly influence soybean yield improvement.