Background and Purpose Effect of endovascular therapy (EVT) in acute large vessel occlusion (LVO) patients with tandem lesions (TLs) within 6–24 hours after last known well (LKW) remains unclear. We evaluated the clinical and safety outcomes among TL-LVO patients treated within 6–24 hours.Methods This multicenter cohort was divided into two groups, based on LKW to puncture time: early window (<6 hours), and late window (6–24 hours). Primary clinical and safety outcomes were 90-day functional independence measured by the modified Rankin Scale (mRS: 0–2) and symptomatic intracranial hemorrhage (sICH). Secondary outcomes were successful reperfusion (modified Thrombolysis in Cerebral Infarction score ≥2b), first-pass effect, early neurological improvement, ordinal mRS, and in-hospital and 90-day mortality.Results Of 579 patients (median age 68, 32.1% females), 268 (46.3%) were treated in the late window and 311 (53.7%) in the early window. Late window group had lower median National Institutes of Health Stroke Scale score at admission, Alberta Stroke Program Early Computed Tomography Score, rates of intravenous thrombolysis, and higher rates for perfusion imaging. After adjusting for confounders, the odds of 90-day mRS 0–2 (47.7% vs. 45.0%, adjusted odds ratio [aOR] 0.71, 95% confidence interval [CI] 0.49–1.02), favorable shift in mRS (aOR 0.88, 95% CI 0.44–1.76), and sICH (3.7% vs. 5.2%, aOR 0.56, 95% CI 0.20–1.56) were similar in both groups. There was no difference in secondary outcomes. Increased time from LKW to puncture did not predicted the probability of 90-day mRS 0–2 (aOR 0.99, 95% CI 0.96–1.01, for each hour delay) among patients presenting <24 hours.Conclusion EVT for acute TL-LVO treated within 6–24 hours after LKW was associated with similar rates of clinical and safety outcomes, compared to patients treated within 6 hours.