Biology doctoral students face a myriad of barriers that may extend or impede their degree completion. These barriers result in a less diverse workforce, considering that institutionalised prejudices have created more barriers to academic success for some groups than others. Here, we aimed to understand the role that non-cognitive and demographic factors play in predicting doctoral students' perceived barriers, and identify which factors best predict personal/psychological, situational, and institutional barriers to degree completion. We surveyed 289 current biology doctoral students in the U.S. We measured grit, sense of belonging, and science identity as well as participants' perceived barriers. We tested the efficacy of non-cognitive factors alone in predicting the three barrier types versus models including demographic factors. We found that both non-cognitive and demographic factors were important in explaining perceived barriers. Higher scores of grit were associated with lower perceived personal/psychological barriers. However, we assert that grittiness is shaped by unique experiences and is highly situational. We do not imply that grit should be used as a main predictor of 'success' in doctoral programs. We suggest future research on what mechanisms facilitate growth of inherently gritty characteristics in biology doctoral students which lead to fewer perceived barriers to degree completion.