Ca²⁺ influx through postsynaptic Ca_v1.x L-type voltage-gated channels (LTCCs) is particularly effective in activating neuronal biochemical signaling pathways that might be involved in Hebbian synaptic plasticity (i.e., long-term potentiation and depression) and learning and memory. Here, we demonstrate that Ca_v1.2 is the functionally relevant LTCC isoform in the thalamus-amygdala pathway of mice. We further show that acute pharmacological block of LTCCs abolishes Hebbian plasticity in the thalamus-amygdala pathway and impairs the acquisition of conditioned fear. On the other hand, chronic genetic loss of Ca_v1.2 triggers a homeostatic change of the synapse, leading to a fundamental alteration of the mechanism of Hebbian plasticity by synaptic incorporation of Ca²⁺-permeable, GluA2-lacking AMPA receptors. Our results demonstrate for the first time the importance of the Ca_v1.2 LTCC subtype in synaptic plasticity and fear memory acquisition.