Are there nonstop flights from Irkutsk (IKT) to Ust-Kut (UKX)?

Yes. UTair Aviation, IrAero fly this route. Flight time is about 1h 7m.

Irkutsk → Ust-Kut

Irkutsk International Airport (IKT) to Ust-Kut Airport (UKX)・518 km

Nonstop flights available (2 airlines). Flight time about 1h 7m. Nonstop return flights also operate.

Times are estimated from distance. Check schedules, frequency and availability with the airline or a booking site.