This study introduces an advanced non-destructive inspection (NDI) technique employing Phased Array Ultrasonic Testing (PAUT) to identify early-stage damage in welds located within orthotropic steel bridge decks. Orthotropic steel bridge decks, renowned for their lightweight and resilient characteristics, are extensively employed in contemporary bridge construction endeavors. Nonetheless, ensuring their structural soundness and detecting flaws holds paramount importance in guaranteeing safety and durability. The initial phases of crack propagation pose challenges for detection through conventional visual inspection methods due to the minute scale of crack dimensions. Nevertheless, adopting preemptive measures during these nascent stages of crack propagation is imperative for reinforcing maintenance protocols and bolstering structural safety measures. A PAUT protocol tailored to the specific characteristics of steel bridge structures is developed through a comprehensive analysis of current non-destructive testing methodologies. Experimental investigations using a specimen validate PAUT’s efficacy in detecting cracks in various weld types, including those between U-ribs and deck plates, U-shaped splice plates and deck plates, and floor beams and deck plates. The results demonstrate PAUT’s ability to identify early damage within steel structures and welds that are not visible to the naked eye, accurately locate defects, determine their size, and identify the direction of crack propagation. The innovative application of PAUT on orthotropic steel bridge decks reflects the maturation and advancement of this technology, offering an effective non-destructive approach for early detection of cracking damage. Prompt identification of potential issues facilitates timely maintenance and reinforcement efforts, ultimately minimizing the risk of human and economic losses.