Given the general absence of suitable direct dating methods, the timing of low-temperature crustal deformation is usually established by indirect methods (such as apatite fission track (AFT) thermochronology), and through relative field-based relationships. U-Pb dating of calcite in tectonic veins represents a recently developed method to directly date brittle deformation. Here, we apply this method to tectonic calcite veins in large scale fault zones in central and western Thailand, in an attempt to shed new light on the regional upper crustal deformation history. U-Pb calcite dates demonstrate tectonic activity at ~216-209 Ma in the Khao Kwang Fold and Thrust Belt associated with the Indosinian stage 2 collision between the Sibumasu and the Indochina Blocks. Brittle deformation along the Three Pagodas Fault Zone has a protracted history, with calcite dates from a single locality at ~45 Ma and ~23 Ma. Petrographic techniques such as reflected light and charge contrast imaging, combined with LA-ICP-MS elemental mapping, are used to relate the U-Pb dates with the paragenesis of the calcite veins in relation to phases of brittle faulting and associated fluid-flow. The veins are interpreted to have formed during multiple hydraulic fracturing events along single fault planes, and exhibit contrasting trace elemental signatures implying fluids with contrasting chemistries have infiltrated the vein arrays during different brittle deformation events. The results from this study advance knowledge on the multi-phase deformation history of Thailand and illustrate the application of combined U-Pb dating and trace element mapping in calcite to unravel complex upper crustal tectonic histories.