Background: The study of children with unilateral cerebral palsy (UCP) has traditionally focused on motor aspects. The extent to which sensory processing disorders can affect their functional performance and quality of life (QoL) is uncertain. This study aimed to explore the differences in sensory processing between UCP and typical development (TD) children and to analyze the relationship of sensory processing with functional performance and QoL. Methods: Fifty-three children aged from 6 to 15 years (TD = 24; UCP = 26) were recruited. The Child Sensory Profile 2, Pediatric Evaluation of Disability Inventory—Computer Adaptive Test and Kidscreen were used to evaluate sensory processing, functional performance and QoL. Results: UCP children showed sensory processing difficulties (avoidance: p = 0.02; registration: p = 0.00; body position: p = 0.00; oral: p = 0.02; social-emotional: p = 0.01), and scored lower in functional performance (daily activities: p = 0.00; mobility: p = 0.00; social/cognitive: p = 0.04) and in physical well-being (p = 0.00). The highest correlations in UCP group were found between proprioceptive processing and daily activities and mobility (r = −0.39); auditory, visual and tactile information and school environment (r = −0.63; r = −0.51; r = −0.46); behavioral and social-emotional responses and psychological well-being (r = −0.64; r = −0.49). Conclusions: UCP children have greater difficulty in sensory processing than TD children. Difficulties in proprioceptive processing contribute to poorer functional performance. Auditory, visual and tactile processing is associated with participation in the school environment and behavioral and social-emotional responses related to sensory processing are associated with the psychological well-being.