There is limited evidence examining the association between physical activity (PA), sedentary time (ST), frailty, and factors influencing PA behaviors in migrant older women from ethnically diverse backgrounds. The aims of this mixed-methods study were to: 1) examine PA levels and ST across frailty status; 2) identify any differences in PA/ST between ethnic and religious groups; and 3) qualitatively explore factors influencing PA among older (≥60 years) migrant women (n = 60). PA/ST were assessed using accelerometry and frailty status using the frailty phenotype. Key factors influencing PA were explored via semi-structured interviews (n = 36) and analyzed using thematic analysis. Participants were highly sedentary irrespective of frailty status. Moderate-to-vigorous-physical activity (MVPA) was independently associated with frailty. Participants spent 69% of waking time in ST, with only 15% meeting current weekly PA recommendations. Health-related and socio-cultural factors were reported as common barriers to achieving PA recommendations. Maintaining independence, preventing physical decline and depression were key factors promoting PA. Understanding the challenges and needs of this population can help to inform strategies to promote PA and thus optimize physical function.