Background: The location of onset of bloodstream infections (BSIs) associated with intensive care unit (ICU) admission may influence their clinical and epidemiological characteristics. Methods: A multicentre, retrospective cohort study was conducted in Queensland, Australia, and BSIs associated with ICU admission were identified and classified as community-onset, hospital-onset, or ICU-onset if first isolated within, after 48 hours but within 48 hours of ICU admission, or after 48 hours following ICU admission, respectively. Results: We included 3,540 episodes of ICU-associated BSI, with 1,693 classified as community-onset, 663 hospital-onset, and 1,184 ICU-onset. Compared with hospital-onset BSIs, patients with ICU-onset BSIs were younger, had fewer comorbidities, had lower APACHE II scores, and were more likely male. Patients with ICU-onset BSI were more likely to be surgical admissions and have a primary cardiovascular or neurological diagnosis. The distribution of infective agents varied significantly among community-, hospital-, and ICU-onset BSI groups. The all-cause 30-day case-fatality rates for first-episode community-onset, hospital-onset, and ICU-onset BSIs were 17.1%, 21.7%, and 23.5%, respectively (p < 0.001). Conclusion: With different epidemiological features and causal pathogens, ICU-onset BSI represents a distinct BSI group arising in hospitalized patients.