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Motor impairments are frequently accompanying core symptoms of autism spectrum disorder (ASD). However, the underlying neural mechanisms subserving impaired motor performance remain understudied, particularly regarding complex and object-directed movements. To investigate this, the study utilised functional magnetic resonance imaging (fMRI) to investigate the neural correlates of motor planning prior to execution, and execution, in adults with ASD (n = 21; M = 26.0 years) and neurotypical (NT) adults (n = 28; M = 27.5 years) during a visually guided, goal-directed, sequential manual task. Task complexity was modulated by the degree of object rotation during the last phase of the task, allowing isolation of neural activation under differing cognitive-motor demands (simple vs. complex). Overlapping brain activation for planning and execution across groups, differences between NT and ASD in planning and execution, respectively, and correlation between brain activation and self-rated autistic traits, were investigated. Analyses were restricted to a mask comprising regions of interest relevant for motor planning and execution, all located in the left hemisphere. Results showed that both phases engaged several posterior parietal and cerebellar subregions in both groups. Compared to the NT group, the ASD group exhibited lower activation of the inferior parietal lobe (IPL) and precentral gyrus during planning, and higher activation of cerebellar lobule IX during execution. Additionally, activation in IPL and cerebellar Crus II were negatively correlated with extent of autistic traits. These findings represent one of the first fMRI investigations of sequential manual performance in adults with ASD.