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The primary objective of this study was to evaluate the capability of a distributed fiber optic sensor to capture in situ dynamic transient strain formation during and post-weldment on the surface of a steel plate. The study involved a vertical manual weld of a bead on a plate on a 300 mm × 300 mm × 6.35 mm A36 steel plate (European equivalent S235J2; Chinese equivalent Q235B) clamped at the corners. A fiber optic distributed sensor was used to measure the surface total and thermal strains on the welded side of the plate adjacent to the weld path. Experimental results show a complex behavior of strain changes during the welding process and the residual strain formation post-welding. This study aims to document the use of distributed fiber optic sensing techniques in welding applications. Validations of the experimental data were performed using VrWeld, a commercial software framework for computational weld mechanics, and an iPhone FLIR One Pro. thermographic camera. The experimental results demonstrated that although distributed fiber optic sensing based on Rayleigh backscattering is an appropriate and useful technique for total strain measurements, the manufacturing and the materials used for the thermal sensors are critical in obtaining optimal results. Finally, this study highlights the challenges encountered in synchronizing large experimental data sets captured with different instruments with computational welding mechanic (CWM) models.