Prior studies have documented that working-class individuals rarely become parliamentarians. We know less about when in the career pipeline to parliament workers disappear, and why. We study these questions using detailed data on the universe of Swedish politicians’ careers over a 50-year period. We find roughly equal-sized declines in the proportion of workers on various rungs of the political career ladder ranging from local to national office. We reject the potential explanations that workers lack political ambition, public service motivation, honesty, or voter support. And while workers’ average high school grades and cognitive test scores are lower, this cannot explain their large promotion disadvantage, a situation that we label a class ceiling. Organizational ties to blue-collar unions help workers advance, but only to lower-level positions in left-leaning parties. We conclude that efforts to improve workers’ numerical representation should apply throughout the career ladder and focus on intra-party processes.