Abstract: Background: Smoking during pregnancy has serious consequences for maternal and child health. An intervention package to embed National Institute for Health and Care Excellence guidance (babyClear©) was delivered across maternity and stop smoking services (SSS) within an English region, to support pregnant women to stop smoking. We aimed to ascertain acceptability among pregnant smokers receiving the intervention. Methods: Pregnant smokers who received the intervention and participated in the study were interviewed, first at around 16 weeks of pregnancy (n = 17) and again several weeks later (n = 8) or postpartum (n = 3). Interview schedules were informed by Normalization Process Theory (NPT) and Theoretical Domains Framework; interviews were audio-recorded, transcribed and analysed thematically, using the Framework method and NPT. Findings are grouped according to the four NPT concepts. Results: Coherence: Carbon monoxide monitoring appeared to make sense; women were motivated to quit by being monitored. Cognitive participation: When linked to a professional discourse of caring and concern, some women were prompted to engage with the SS message. Women were more guarded in their reaction to initial contact from the SSS; reporting attending appointments successfully, or in some cases, experiencing problems that decreased engagement and made quitting harder. Collective action: Where women continued to smoke or failed to attend SSS appointments, an extra intervention was delivered, the Risk Perception Tool (RPT), which often prompted pregnant women to act. Reflexive monitoring: Most women accepted the need for a hard-hitting approach (RPT) and, while it distressed them at the time, they claimed they were subsequently grateful for it. SSS intervention post-RPT was seen as supportive, partly because it often involved home visits. Aspects of family inclusion in babyClear© were reported as beneficial. In Trusts where women experienced services as less focused on prioritising the stop smoking message, less well integrated or reported maternity staff as less adept at delivering the RPT, women found babyClear© less acceptable overall. Conclusions: The babyClear© package was acceptable to pregnant smokers interviewed during and shortly after pregnancy and, in some cases, to promote quitting. However, some contexts were more optimal than others, leading to variation in acceptability overall.