This article presents four studies aimed at developing a Polish-language version of the newest measure of life satisfaction, i.e., the English-language Riverside Life Satisfaction Scale (RLSS), and efforts towards its further validation. The pre-final Polish version of the RLSS (RLSS-PL) established in Study 1 was subsequently investigated in three online validation studies. In these studies, we replicated the findings obtained by the authors of the original RLSS regarding the unidimensionality of RLSS-PL and its high internal consistency. We also determined the correlations between the RLSS-PL and other measures including life satisfaction, affect balance, positive and negative affect, psychological well-being, subjective happiness, personality traits, values, socially desirable responding, awareness of the research hypothesis, and demographic characteristics. Further validation of the RLSS-PL involved our establishing correlations between the RLSS-PL and previously unanalyzed psychological constructs such as social and emotional well-being, gratitude, self-esteem, positive orientation, and mindfulness. In addition, we have determined the test-retest stability of the RLSS-PL over three-month and six-month intervals. The findings provided evidence that the RLSS-PL is a unidimensional, valid, reliable, and stable measure of life satisfaction in reference to the Satisfaction With Life Scale (SWLS).