Determining effective decision support strategies that enhance quality of end-of-life decision making in the intensive care unit is a research priority. This systematic review identified interventional studies describing the effectiveness of decision support interventions administered to critically ill patients or their surrogate decision makers. We conducted a systematic literature search using PubMed, CINAHL, and Cochrane. Our search returned 121 articles, 22 of which met the inclusion criteria. The search generated studies with significant heterogeneity in the types of interventions evaluated and varied patient and surrogate decision-maker outcomes, which limited the comparability of the studies. Few studies demonstrated significant improvements in the primary outcomes. In conclusion, there is limited evidence on the effectiveness of end-of-life decision support for critically ill patients and their surrogate decision makers. Additional research is needed to develop and evaluate innovative decision support interventions for end-of-life decision making in the intensive care unit.