Background: Increasing interest and participation in engineering is vital if the United States is to create the larger technological and scientific labor force it needs to meet the challenges of the 21st century. Students' pathways into the different engineering majors provide important information for this effort. Purpose: This study addresses which factors across life stages (pre-high school, high school, and early college) are associated with engineering major choice. The quantitative analysis identifies which demographic characteristics and academic achievement variables are correlated with engineering major choice, whereas the qualitative analysis examines when and why students choose a specific engineering major. Methods: Informed by the life course perspective, this convergent mixed methods research study applies Logit regression and thematic analysis. Data sets include more than 20,000 observations of student-level academic records (2001-2015) as well as interviews conducted with 20 students at a large, research-intensive university in the Midwest. Results: Quantitative results indicate that student demographic factors and measures of academic achievement--including passing scores on advanced placement tests, scholastic aptitude test scores, and high school and college first-year grade point averages--are associated with engineering major choice. Qualitative findings show that across the life stages, the source of social influence in engineering major choice varies; while family and teachers play larger roles before and during high school, peers and university personnel play larger roles in early college. Conclusion: The conceptual model comprehensively synthesizes the key factors associated with engineering major choice, highlighting the importance of demographic factors, academic achievement, social networks, and access to role models from pre-high school, high school, and early college.