Procrastination is prevalent among students and is associated with negative outcomes, including poor academic performance and psychological distress. Research also suggests that anxiety and depression can exacerbate procrastination; however, the mechanisms associated with the development of procrastination are less understood. The current study aimed to clarify the role of negative repetitive thought (i.e., rumination and worry) in the links between anxiety and procrastination, and depression and procrastination. Ninety-one undergraduate students completed self-report measures of anxiety, depression, worry, brooding rumination, and procrastination, and two multiple mediator models were tested. Procrastination was positively correlated with the study variables, including medium effects for anxiety and depression, a large effect for rumination, and a small effect for worry. Rumination independently mediated the relationships between anxiety and procrastination, and depression and procrastination. Worry did not independently mediate these relationships. The current findings suggest rumination plays a larger role in the links between anxiety, depression, and procrastination than worry. Thus, students with higher levels of anxiety and depression engage in more negative repetitive thought, which may contribute to procrastinatory behavior as a result of a preoccupation with depressing or painful thoughts about the past.