Abstract Background The recent resurgence of malaria in western Thailand has coincided with increased cross-border migration from Myanmar following political unrest. As short-term migrants from endemic areas may contribute to sustained local transmission, this study examined their malaria care-seeking behaviours and infection prevalence. Methods A community-based cross-sectional study was conducted during March–April 2025 in six malaria-endemic villages of Tha Song Yang District, Tak Province, western Thailand. A structured questionnaire was administered, including a nine-item section on care-seeking behaviours. Malaria prevalence was determined by PCR testing of dried blood spot samples. Determinants of care-seeking scores were analysed using a generalized linear model, and infection risk was estimated using Firth logistic regression. Results Among 300 participants (mean age: 34.5 ± 14.5 years; 47.3% male), over 60% recognised the need to seek care for fever or chills, yet only 35% reported doing so within 24 h of symptom onset. Although 98.0% preferred public health facilities, only 50.3% had ever visited one for suspected malaria. Higher care-seeking scores were associated with being a daily wage labourer (β = 0.66; 95% CI 0.01–1.31), infrequent return to Myanmar (β = 1.34; 95% CI 0.05–2.62), prior malaria experience (β = 1.08; 95% CI 0.59–1.58), and higher malaria knowledge (β = 0.34; 95% CI 0.24–0.44). Karen ethnicity was negatively associated with care-seeking (β = − 0.95; 95% CI − 1.74 to − 0.16). Six (2%) afebrile Plasmodium vivax infections were detected. Lower malaria knowledge (OR = 13.5; 95% CI 1.58–177.0) and care-seeking scores (OR = 5.86; 95% CI 1.15–57.7) were significantly associated with infection. Conclusions Despite generally positive attitudes toward malaria, self-reported timely care-seeking among short-term Myanmar migrants remained limited. Socioeconomic status, migration patterns, ethnicity, and malaria knowledge significantly influenced care-seeking behaviours. The detection of asymptomatic P. vivax underscores the need for migrant-focused surveillance and targeted health education to support malaria elimination efforts.