Excessive gestational weight gain (GWG), defined as exceeding the recommended pregnancy weight gain for Body Mass Index (BMI), is experienced by approximately 50% of women and is associated with negative health outcomes for both the mother and baby. The primary aim of this study was to evaluate the efficacy of a Health Coaching (HC) intervention designed to prevent excessive GWG compared to a matched convenience control sample that received usual care. The secondary aim was to evaluate improvement in psychosocial, motivational and behavioural factors as a result of the HC intervention. Pregnant women were recruited from two tertiary hospitals in Melbourne, Australia. A total of 116 HC participants and 131 control participants agreed to participate in the study; 116 HC women and 127 controls returned baseline questionnaires (16-18 weeks gestation), and 81 HC and 102 controls returned follow-up questionnaires (32 weeks gestation). In addition to their usual antenatal care, women in the intervention group received four HC and two educational sessions based on health behaviour change theories; women in the control group received only their usual antenatal care. Objective weight measures were collected throughout pregnancy. Despite a trend in the data revealing that a greater percentage of control women gained weight excessively, there was no significant difference between the groups in the rate of excessive GWG after accounting for pre-pregnancy BMI, parity, baseline weeks gestation, depressive symptoms, diet and physical activity motivation, and coping skills. However, at 32 weeks gestation (post-intervention), intervention women reported greater use of active coping skills, and women who completed the full intervention also reported greater body satisfaction and vegetable intake.Therefore, a HC intervention during pregnancy may be effective at improving psychosocial and behavioural aspects of health that may lead to reduced incidence of excessive GWG. The theoretical and practical implications of this study are discussed.