Applying social investment theory (SIT), we examined whether employment trajectories until midlife, with differential investments in education and employment, are associated with social investments during early life and with work-related well-being in midlife, with a special reference to potential differences between self-employment and paid work. In the Northern Finland Birth Cohort 1966 (n = 6496; 2963 men, 3533 women), life-history calendars from age 16 to 45 were used to determine the respondents’ yearly employment statuses (student, full-time employee, part-time employee, self-employed, unemployed, on parental leave, on sabbatical leave or otherwise not working). Latent class analysis was used to identify the employment trajectories. The associations of these trajectories with indicators of social investments in early life (mother’s attitude to financial self-reliance, father’s socioeconomic status, own success at school) and work-related well-being at age 46 (job satisfaction, life satisfaction, absence of retirement thoughts, work engagement, work favoring attitude and perceived job control) were studied using regression models and analyses of variance, adjusting for life situation at age 46. We identified five employment trajectories for both genders: 1) traditional full-time, 2) highly educated, 3) self-employed, 4) delayed full-time and 5) floundering employees. In early life, a mother emphasizing self-reliance in earning one’s living was associated with both highly educated and self-employed trajectories. A white-collar father and own success at school preceded a highly educated trajectory. A farmer family background preceded self-employed trajectory. At age 46, highly educated and self-employed trajectories were associated with highest well-being at work, while those floundering perceived their work most negatively. Men in the delayed full-time employment trajectory reported better well-being at age 46 than those constantly floundering. Overall, the macroeconomic employment rates were unevenly reflected in the five trajectories. Our findings support SIT by showing that the employment trajectories most favorable for work-related well-being in midlife are long rooted in social investments during early life and characterized by further social investments in employment, such as higher education and self-employment.