There have been no published randomized clinical trials with a primary outcome of socioeconomic inclusion for young people who have experienced homelessness. To explore whether young people exiting homelessness who received rent subsidies and adult mentorship experienced more socioeconomic inclusion relative to young people who received only rent subsidies. This was a convergent mixed-methods, unblinded, 2-group, parallel randomized clinical trial with 1:1 allocation embedded within a community-based framework in 3 cities in Ontario, Canada. Participants were enrolled between March 1 and September 30, 2019, and were followed up through March 31, 2022. Participants (n = 24) were randomly assigned adult mentors (n = 13) who had been recruited and screened by community partner agencies. All participants received portable rent subsidies (subsidy not tied to a specific location) for 2 years. Primary quantitative outcomes were self-reported measures of community integration (psychological and physical) and self-esteem-proxy indicators of socioeconomic inclusion. Community integration was measured with the Community Integration Scale, with a score range of 1 to 7 for the physical component and 4 to 20 for the psychological component; higher scores indicate higher integration. Self-esteem was measured with the Rosenberg Self-Esteem Scale, with a score range of 0 to 30; higher scores indicate greater self-esteem. Secondary quantitative outcomes included social connectedness, hopelessness, and academic and vocational participation. All analyses followed the intention-to-treat principle. A total of 24 youths (12 women [50.0%]; mean [SD] age, 21.8 [2.2] years [range, 18-26 years]; race and ethnicity: 10 White [41.7%], 8 Black [33.3%], 2 Asian [8.3%], 2 Indigenous [8.3%], and 2 different choice [8.3%]) transitioned out of homelessness and into market-rent housing. All youths in the group that received mentorship and in the group that did not receive mentorship had stable or nonsignificant improvements in all study outcomes at the primary end point of 18 months compared with baseline (mean [SD] Community Integration Scale psychological score: mentorship group, 11.3 [2.6] at baseline and 11.2 [3.9] at 18 months; no-mentorship group, 10.8 [4.1] at baseline and 13.2 [2.9] at 18 months; mean [SD] Rosenberg Self-Esteem Scale score: mentorship group, 16.0 [4.6] at baseline and 18.1 [5.2] at 18 months; no-mentorship group, 16.3 [6.1] at baseline and 19.6 [5.7] at 18 months). However, there were no significant differences between the 2 groups in the Community Integration Scale psychological score (adjusted mean difference, -2.0; 95% CI, -5.0 to 1.0; P = .18) and Rosenberg Self-Esteem Scale score (adjusted mean difference, -1.4; 95% CI, -5.0 to 2.3; P = .44) 18 months after randomization. Ancillary analysis suggested that youths with informal mentors (mentors outside the study) at baseline felt more psychologically integrated at 18 months relative to those with no informal mentors at baseline (adjusted mean difference, 3.6; 95% CI, 0.4-6.8; P = .03). In this randomized clinical trial, COVID-19 pandemic-related restrictions made it challenging for mentors and mentees to connect, which may have affected the findings. Steady socioeconomic outcomes-potentially attributable to portable rent subsidies-are noteworthy, given the socioeconomic inequities this population has faced during the COVID-19 pandemic. The possible benefit of informal mentorship warrants further investigation. This small pilot study was designed with the intention of generating data and hypotheses for a full-scale study; findings should be interpreted with caution. ClinicalTrials.gov Identifier: NCT03779204.