This study investigated the development of novel metaphor and metonymy comprehension in both typically developing (TD) children and individuals with Williams syndrome (WS). Thirty-one TD children between the ages of 3;09 and 17;01 and thirty-four individuals with WS between the ages of 7;01 and 44 years old were administered a newly developed task examining novel metaphor and metonymy comprehension, as well as a range of standardised tests that assess semantic knowledge. This age range and the background measures allowed construction of developmental trajectories to investigate whether chronological age or mental age, represented by word knowledge, relate to novel metaphor and metonymy comprehension. The results showed that comprehension of figurative language did not increase with chronological age in WS, in contrast to TD. Although there was no difference for the different types of metaphors, certain metonymy expressions were found to be easier than others in the TD group. In addition, semantic knowledge was a reliable predictor for novel metaphor and metonymy comprehension in the TD but only for metonymy in the WS group. In sum, development of novel metonymy in the WS group is only delayed while comprehension of novel metaphor is both delayed and atypical. However, future research should further investigate differences between sub-types, as well as what cognitive factors relate to novel metaphor comprehension in individuals with Williams syndrome. (Contains 3 figures and 2 tables.)