The current study was designed to investigate the concurrent and temporal associations between petitionary-focused prayer for a partner and relationship outcomes such as relationship satisfaction, commitment and quality, romantic loneliness, and relationship disillusionment from the perspective of the moderating role of relationship form (marital vs. nonmarital relationship). This study utilized a cross-sectional and longitudinal design and examined 412 Polish adults aged 18–75 (M = 35.10, SD = 9.50) at Time 1 and 190 participants after a four-month interval. The results revealed a moderation function of relationship form at T1 for relationship satisfaction at T1 and that more praying for a partner at T1 was associated with higher relationship satisfaction at T1 in marital relationships but not in nonmarital relationships. There was, however, a trend suggesting that more praying for a partner at T1 might be related to lower levels of romantic loneliness at T2 in marital relationships but not in nonmarital relationships. No interaction effects were observed for other relationship outcomes. These results suggest that the effects of praying for a partner may differ depending on relationship outcomes and that prayer may play a positive function with respect to relationship satisfaction in marital relationships in comparison to nonmarital relationships.