BACKGROUND: Contraceptive use among young women in Nairobi remains low despite high general knowledge of family planning (FP) methods. This paper draws on social norms theory to explore the role of key influencers (partners, parents and friends) in women's FP use and how women anticipate normative reactions or sanctions. METHODS: A qualitative study with 16 women, 10 men and 14 key influencers across 7 peri-urban wards in Nairobi, Kenya. Interviews were conducted during the COVID-19 pandemic in 2020 by phone. A thematic analysis was conducted. RESULTS: Women identified parents, specifically mothers, aunts, partners, friends and healthcare workers as key influencers on FP. Their interactions with these key influencers varied based on trust, the information they needed about FP, and whether they perceived a key influencer to perpetuate or challenge existing social norms on FP. Mothers were perceived to understand the social risks of using FP and thus could advise on discreet FP use, and aunts were trusted and approachable sources to impartially describe the benefits and drawbacks of FP. Although women identified partners as key FP decision makers, they were cognisant of possible power imbalances affecting a final FP choice. CONCLUSIONS: FP interventions should consider the normative influence key actors have on women's FP choices. Opportunities to design and deliver network-level interventions which seek to engage with social norms surrounding FP in order to challenge misconceptions and misinformation among key influencers should be explored. Intervention design should consider dynamics of secrecy, trust and emotional closeness that mediate discussions of FP to address changing norms. Further training to change norms held by healthcare providers about why women, in particular unmarried young women, access FP should be provided to reduce barriers for FP access.