Abstract Background We investigated the acceptability and feasibility of a new brief intervention for maternal prenatal anxiety within maternity services in London and Exeter, UK. Methods One hundred fourteen pregnant individuals attending their 12-week scan at a prenatal clinic with elevated symptoms of anxiety (GAD-7 score of ≥7) were randomly assigned to either the ACORN intervention + Treatment as usual (TAU) (n = 57) or to usual care only (n = 57). The ACORN intervention consisted of 3 2-h group sessions, led by a midwife and psychological therapist, for pregnant individuals and their partners. The intervention included psychoeducation about anxiety, strategies for problem-sovling and tolerating uncertainty during pregnancy, including communicating about these with others, and mindfulness exercises. Results Engagement rates with ACORN met or exceeded those in primary care services in England. In the intervention arm, 77% (n = 44) of participants attended at least one session, 51% (n = 29) were adherent, defined as attending two or more sessions. Feedback was positive, and participants in the ACORN treatment group demonstrated evidence of a larger drop in their levels of anxiety than the participants in the TAU-only group (Cohen’s d = 0.42). Conclusion The ACORN intervention was acceptable to pregnant individuals and their partners and resulted in reductions in anxiety. With further evaluation in a larger-scale trial with child outcomes, there is significant potential for large scale public health benefit.