Prospective memory (PM) is the ability to execute future intended actions and may be negatively affected by impulsivity. The current study aimed to address questions on (1) relationships of PM with facets of impulsivity; (2) psychometric properties of a PM task, in particular convergent validity with self-reported PM; and (3) whether external support of the encoding process would improve PM or affect relationships with impulsivity. 245 participants performed the experiment online. Participants completed either a baseline version of the task, which combined blocks of an ongoing working memory task with PM trials involving a varying stimulus requiring an alternative response; or a version that provided external support of encoding by requesting that participants visualize and execute the intended prospective action before each block. The Prospective-Retrospective Memory Questionnaire (PRMQ) and Short Version of the UPPS-P Impulsive Behavior Scale (SUPPS) were used to assess self-reported prospective memory and facets of impulsivity. Reliability of PM performance was good and remained acceptable even with the exclusion of participants with low scores. PM performance was associated with self-reported PM, explaining variance in addition to that explained by working memory performance. PM performance was also negatively associated with impulsivity, in particular sensation seeking and positive urgency, but only in the baseline task. Support did not cause overall improvements in performance. In conclusion, results provided further evidence for a relationship between facets of impulsivity and PM. PM as assessed via the current task has good psychometric properties.