Purpose Lifitegrast is a lymphocyte function–associated antigen-1 antagonist developed to reduce inflammation in dry eye disease (DED). We report the results of OPUS-3 (NCT02284516), a phase III study evaluating the efficacy and safety of lifitegrast versus placebo in participants with DED. Design Twelve-week, phase III, randomized, double-masked, multicenter, placebo-controlled study. Participants Adults aged ≥18 years with Schirmer tear test (without anesthesia) ≥1 and ≤10 mm, corneal fluorescein staining score ≥2.0 (0–4 scale), eye dryness score (EDS) ≥40 (0–100 visual analogue scale [VAS]), and history of artificial tear use within 30 days of study entry. Methods After a 14-day placebo run-in, participants were randomized 1:1 to lifitegrast ophthalmic solution 5.0% or placebo twice daily for 84 days. Main Outcome Measures The primary efficacy end point was change from baseline to day 84 in EDS. Key secondary efficacy end points were change from baseline to days 42 and 14 in EDS. Other secondary efficacy end points included additional VAS items (burning/stinging, itching, foreign body sensation, eye discomfort, photophobia, pain), ocular discomfort score (ODS), and safety/tolerability of lifitegrast versus placebo. Results In the study, 711 participants were randomized: placebo, 356; lifitegrast, 355 (intention-to-treat [ITT] population). At day 84, lifitegrast-treated participants experienced significantly greater improvement from baseline in EDS versus those receiving placebo (treatment effect [TE], 7.16; 95% confidence interval [CI], 3.04–11.28; P = 0.0007). Mean changes from baseline in EDS also significantly favored lifitegrast on days 42 (TE, 9.32; 95% CI, 5.44–13.20; P < 0.0001) and 14 (TE, 7.85; 95% CI, 4.33–11.37; P < 0.0001). No statistically significant differences were observed in ODS between treatment groups at days 84, 42, or 14. A greater improvement was observed in lifitegrast-treated participants at day 42 in itching (nominal P = 0.0318), foreign body sensation (nominal P = 0.0418), and eye discomfort (P = 0.0048) versus participants receiving placebo. Most treatment-emergent adverse events were mild to moderate in severity; no serious ocular adverse events were reported. Conclusions Lifitegrast significantly improved symptoms of eye dryness, as measured by EDS, versus placebo in participants with DED. Improvement in EDS was observed as early as day 14. Lifitegrast appeared well tolerated.