Chemsex, a form of sexualized drug use, is prevalent among men who have sex with men (MSM) in the United Kingdom (UK), contributing to public health concerns like increased HIV transmission and overdose risk. This study explored the link between early first anal sex and chemsex engagement among MSM, a connection that has been underexplored in the UK. Analyzing data from 10,702 UK-based MSM from the European MSM Internet Survey (EMIS-2017), we used ordinal and binomial logistic regressions to assess how the age of first anal intercourse correlated with sexual risk behaviors and chemsex. The median age of anal sex debut was 17, with most participants (65%) reporting their first experience at 18 or older. A smaller group (7%) had their first anal intercourse at 13 or younger. Compared to those who had their first anal sex at 18 years or older, MSM who initiated anal sex at 17 years or younger were more likely to report having more non-steady condomless intercourse partners (aOR = 1.46, p < .001), using chemsex-associated drugs (aOR = 1.26, p = .013), engaging in non-sober sex (aOR = 1.22, p < .001), and recent involvement in chemsex (aOR = 1.48, p < .001). These findings highlight the need for interventions that address early sexual experiences to reduce sexual risk behaviors and chemsex among MSM.