An Gaiser has a background in social work and started her career as a probation officer. She was involved in reporting and advising the court on the problems of suspects and their risk of recidivism. She also accompanied ex-prisoners for many years. After more than nine years, she switched to the General Intelligence and Security Service (AIVD), where she worked until 2019. In this role she applied her knowledge and experience as a security researcher and screener in politically sensitive environments. In 2017 she also became Managing Partner of the Institute for Non-verbal Strategy Analysis. Between February 2022 and February 2023, An Gaiser was also Senior Manager Forensic Integrity & Compliance at KPMG. Since 2021 An also runs her own consultancy firm, An Gaiser Consultancy.