Those making suicide attempts with highly lethal medical consequences are arguably the best proxy for those who die by suicide and represent a qualitatively different population from those making lower lethality attempts. Different factors influence the likelihood of a suicide attempt occurring and the lethality of that attempt. Both are important dimensions of risk. Older adults represent a distinct group in suicide research with unique risk factors that influence the lethality of their suicide attempts. This systematic review and meta-analysis summarises factors distinguishing those making high and low-lethality suicide attempts in older adulthood. Databases PsycINFO, PubMed (MEDLINE), Embase and CINAHL were systematically searched with seven of 1182 unique records included. Random effects meta-analyses were conducted on 18 variables in addition to a narrative synthesis regarding executive function. Only increased suicidal intent and planning meaningfully distinguished high from low-lethality attempters in meta-analyses. A large effect size was additionally observed for white ethnicity. Diminished alcohol use disorder prevalence and depression severity, and greater cognitive impairment, may be associated with high lethality attempters but further research is needed. Age and gender were not associated with lethality, contrary to adult populations. A narrative synthesis of studies exploring differences in executive functioning suggested high-lethality attempters were less likely to impulsively act on suicidal urges, allowing them to better plan suicide attempts that are more lethal, and are less likely to alter suicidal plans. Key limitations were that meta-analyses were underpowered to detect small effect sizes, and samples were largely white and limited to the USA.