Reactive oxygen species (ROS) are integral components of plant signaling networks that mediate interactions between plants and their environment, thereby regulating diverse physiological and biochemical processes. While controlled ROS production is essential for stress perception and signal transduction, excessive ROS accumulation induces oxidative damage. ROS-mediated lipid peroxidation of polyunsaturated fatty acids leads to the formation of highly electrophilic α,β-unsaturated carbonyl compounds collectively referred to as reactive carbonyl species (RCS). Under severe abiotic stress conditions, excessive RCS accumulation exerts cytotoxic effects and causes widespread cellular dysfunction. In contrast, at subtoxic levels, RCS function as important secondary messengers that modulate stress-responsive signaling pathways, including programmed cell death, stomatal regulation, and adaptive responses to abiotic stresses. This review critically synthesizes current advances in understanding the dual roles of ROS and RCS as both damaging agents and signaling molecules in plants. Particular emphasis is placed on the mechanistic basis of ROS-RCS crosstalk and their interactions in abiotic stress tolerance. Furthermore, this review highlights emerging research gaps and outlines future perspectives aimed at translating redox signaling insights into strategies for improving plant stress resilience under changing environmental conditions.