Gas turbine engines operate at extreme temperatures above 900 °C, requiring thermal barrier coatings (TBCs) to protect engine components. TBCs consist of a metallic bond coat, a thermally grown oxide (TGO) layer, and a ceramic top coat (TC). Their failure can severely impact engine reliability, making the understanding of their micro-mechanical properties crucial for resistance to mechanical stresses, deformation, cracking, and delamination. This study aimed to acquire localised mechanical properties and microstructural information to better understand sub-surface TBC failures, using advanced characterisation methods, providing data for improved lifetime predictions. Microstructural and compositional analyses were conducted using scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS). This research performed micro-pillar compression tests on TBCs and used plasma-focused ion beam (PFIB) milling for high-resolution 3D reconstruction of the TBC microstructure. These techniques allow for unprecedented insights into the localised behaviour of TBC layers. Influence of ageing conditions was studied through SEM imaging and EDS analysis, revealing increasing ageing time (8 hours to 1000 hours) caused severe degradation, compared to increasing temperature (950 °C to 1100 °C). PFIB data collection for 3D reconstruction yielded high-resolution datasets, though 3D segmentation of microstructural features such as cracks was unsuccessful. Micropillar compression testing methodology was developed to understand localised failure mechanisms. In-situ qualitative data was obtained on the localised failure mechanisms in the micropillars during compression. The mechanical response of pillars containing TGO varied due to different proportions of TBC layers. Notably, pillars from samples aged at 1100 °C for 8 h showed significantly lower ultimate compressive strength compared to those aged at 950 °C for 8 hours. The preferential crack pathway was found at the TC/TGO interface. This study provides essential insights into the micro-mechanical behaviour and failure mechanisms of TBCs, which are critical for enhancing their durability and predicting their lifetime under various operational conditions.