This thesis examines how Big Data reshapes consumer behaviour analysis and transforms digital marketing strategy. It integrates a comprehensive literature review with a practical, data-driven exploration using a synthetic consumer dataset. The study highlights how advanced analytics strengthen personalization, segmentation, and real-time decision-making across industries, while also exposing ethical challenges tied to privacy, transparency, and algorithmic bias. Methodologically, the thesis adopts a mixed-design approach that combines qualitative literature insights with quantitative data visualizations to bridge theory and practice. Its motivation lies in addressing the gap between behavioural understanding and strategic implementation, with the objective of demonstrating how big data can elevate digital marketing effectiveness in a real-world context.