Aim This study evaluated the relationship between picky eating, mindful eating (ME), orthorexia nervosa (ON) tendency, and diet quality in adults. The secondary aim was to examine whether picky eating mediates the effect of ME on ON tendency. Methods A total of 541 adults (mean age 26.6 ± 10.54 y, 50.6% women) participated. Data were collected using a structured questionnaire via face-to-face interviews and convenience sampling. Picky eating (PE) was assessed with the Adult Picky Eating Questionnaire, ME with the ME Inventory (MEI), ON tendency with the Test of ON-17 (TON-17), and diet quality with the Healthy Eating Index-2020. Dietary intake was measured using a 24-h dietary recall. Results Among participants, 5.2% had ON, and 41.6% had inadequate diet quality. MEI was positively associated with PE ( β = 0.108; P = 0.013) and TON-17 ( β = 0.093; P = 0.025). PE was positively associated with TON-17 ( β = 0.213; P < 0.001) and negatively associated with Healthy Eating Index-2020 ( β = –0.126; P = 0.003). The indirect effect of MEI on TON-17 via PE accounted for 19.8% of the total effect, indicating that PE partially mediated this relationship. Conclusions The findings suggest that ME is associated with healthier dietary behavior; however, they may also be related to increased orthorexic tendencies. It also showed that PE mediates between MEI and TON-17. Addressing selective eating behaviors and encouraging balanced, ME in public health strategies may help improve diet quality and reduce eating related problems.