Children diagnosed with autism spectrum disorder (ASD) are at increased risk of persistent language and literacy difficulties. This study investigated the effectiveness of an 8-week parent-implemented shared book reading intervention designed to change parent and child book reading behaviours. Sixteen parents and their preschoolers on the autism spectrum participated. Nine parents were randomly allocated to receive the shared book reading intervention first. The intervention used a coaching model and comprised a training session, four home visits, and four follow-up phone calls. Parents completed a shared book reading video with their child prior to the intervention, immediately post-intervention and eight weeks after the intervention was completed. Following intervention, there was a significant increase in the intervention group parents' use of book-related vocabulary and their explicit teaching of story structure, compared to the waitlist control group. Compared to the control group, there was a significant increase in children's verbal participation (number of utterances and number of different words). However, these effects disappeared when the significant increase in reading duration following the intervention was taken into account. All improvements were maintained over time. Our results highlight the feasibility of a parent-implemented shared book reading intervention for encouraging early language skills in children on the spectrum in a naturalistic setting that is part of many family routines.