ACS (1-aminocyclopropane-1-carboxylic acid synthase) is a member of the aminotransferase superfamily and a pyridoxal phosphate-dependent enzyme. ACS is also a rate-limiting enzyme for the biosynthesis of ethylene and has been linked with plant development, growth, and stress responses. However, information on ACS genes in the soybean genome is limited. In this study, we identified ACS genes in soybean through phylogenetic trees and conserved motifs and analyzed their cis-acting elements, subcellular localization, and expression patterns. Twenty-two members of the ACS family were identified in soybean, and they were divided into four subfamilies based on phylogenetic relationships. Moreover, the results of Arabidopsis mesophyll protoplasts showed that GmACS1, GmACS8, and GmACS15 were all localized in the nucleus and cell membrane. Cis-regulatory elements and qRT-PCR analyses indicated markedly increased levels of GmACS transcripts under hormone treatments and abiotic stress conditions (drought, alkalinity, and salt). In addition, under different abiotic stresses, the potential functional variations across the GmACS isoforms were mirrored in their differential expression. The analysis of transcriptional response to salinity indicated that salt stress might primarily be mediated by the GmACS15 gene. GmACS15 was also found to reduce salt-induced oxidative damage by modulating the ROS-scavenging system, cellular redox homeostasis, and maintaining intracellular Na⁺/K⁺ balance. The results of this investigation revealed the involvement of the ACS gene family in soybean stress-response pathways, including the identification of a potential target for enhancing salt tolerance in soybean.