Despite supportive structural changes to reduce stigma towards lesbian, gay, and bisexual, transgender, queer, and questioning (LGBTQ) Canadian residents, sexual minority youth still face disparities compared to heterosexual peers. We aimed to characterize LGBTQ-supportive environments and political climates, and examine their links to suicidal behavior among sexual minority adolescents in western Canada. Data were from the 2013 British Columbia Adolescent Health Survey, a cluster-stratified random cross-sectional survey of public school students in BC, Canada; We sampled 2678 self-identified LGB and mostly heterosexual students (69% girls) from 274 schools, representing an estimated provincial population of 24,624 sexual minority students in weighted models. Student reports of past-year suicidal ideation, suicidal attempts, and self-harm behaviors were merged with community-level data assessing diverse aspects of LGBTQ-supportive resources and progressive political climates in communities surrounding the schools. Adjusted multilevel models showed that for sexual minority adolescent girls, higher community LGBTQ-supportiveness predicted marginally significant lower suicidal ideation (aOR = 0.94, 95% CI [0.88, 1.01]) and suicidal attempts (aOR = 0.91, 95% CI [0.83, 1.00]) and significantly lower self-harm behaviors (aOR = 0.91, 95% CI [0.85, 0.98]). Further, progressive political climates predicted marginally significant lower suicidal ideation (aOR = 0.89, 95% CI [0.78, 1.02]) and significantly lower self-harm behaviors (aOR = 0.87, 95% CI [0.77, 0.99]). For sexual minority adolescent boys, no community-level variables were associated with suicidal behavior in adjusted models. Thus, LGBTQ-supportive communities and progressive political climates appear to be protective against suicidal behavior among sexual minority adolescent girls, but not sexual minority adolescent boys.