Background <p>The woman’s choosing the birth support partner herself increases her satisfaction, comfort and positively affects the process. Moreover, when the health staff provides supportive care to a woman, her physical comfort and satisfaction with birth, and the quality of care increase. This study aimed at investigating effects of companion support during labor on pregnant women’s birth comfort, satisfaction, and postpartum comfort.</p> Methods <p>This randomized controlled trial was conducted in Training and Research Hospital between March 01-September 30, 2023 and 104 primigravidae were included. They were assigned to the intervention and control groups in equal numbers. The women in the intervention group received companion support during labor, whereas women in the control group received standard hospital care.</p> Findings <p>The Birth Satisfaction Scale total score and its sub-dimensions quality of care provision, women’s personal attributes, and stress experienced during labor were significantly higher in the intervention group than in the control group (<i>p</i> &lt; 0.05). Similarly, Childbirth Comfort Questionnaire scores were higher in the intervention group (<i>p</i> &lt; 0.01), with a particular increase observed in the psychospiritual comfort subdimension. Postpartum Comfort Scale total scores and its subdimensions physical, psychospiritual, and sociocultural comfort were also significantly higher among women in the intervention group compared to the control group (<i>p</i> &lt; 0.05).</p> Conclusions <p>The results of the study revealed that companion support during the birth process played a significant role in increasing women’s birth comfort and satisfaction, and that companion support should be encouraged in health policies in order to improve birth services and to provide better support to pregnant women.</p> Trial registration <p>ClinicalTrials.gov, NCT06624748. Registered on 3 January 2023.</p>