The beginning of the COVID-19 pandemic brought about a sudden and significant change in the conditions of various academic activities. In the present study, we wanted to investigate the influence of the first pandemic lockdown on procrastination tendencies among Polish students. To achieve this goal we employed a mixed-method, embedded longitudinal study. In the quantitative part of the research, the same group of university students completed the procrastination questionnaire twice: a year before, and two months after the introduction of the first pandemic lockdown. The qualitative part included the open-ended questions about the perceived reasons for an observed change in a tendency to postpone tasks after the pandemic outbreak. Our analyses showed a significant increase in academic procrastination after the lockdown introduction. In particular, students reported a decrease in the study interest and lower working discipline. As the causes of higher procrastination during the lockdown period, students most frequently pointed out the reduced monitoring of work progress by supervisors and lower negative consequences of delaying tasks. The second most frequent theme in provided answers included difficulty in restraining from alternative activities and problems with focusing on tasks or ignoring distractions. Embedding qualitative and quantitative data gave a consistent picture of students' situation in the first lockdown and provided potential explanation for the exacerbation of procrastinatory behaviors after the pandemic outbreak.