Date: 202012
Local time of day: 1201-1800
Location: ZZZ.Airport, US
Flight conditions: VMC
Aircraft: A320
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Taxi
ATC / advisory: Tower ZZZ
Second aircraft: Any Unknown or Unlisted Aircraft Manufacturer
Reporter organization: Air Carrier
Reporter function: First Officer
Reporter qualification: Flight Crew Multiengine; Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument
Human factors: Situational Awareness; Confusion; Communication Breakdown; Distraction
Second reporter function: Captain
Anomaly: Deviation / Discrepancy - Procedural Clearance; Ground Incursion Runway
Result: General None Reported / Taken
Contributing factors: Human Factors
Primary problem: Human Factors

Narrative: The timing of the situation was ripe for a mistake; as a similar-sounding call sign received the exact type of clearance we would have expected as we approached the end of the runway while I was task saturated with completing the required checklist. Ideally; I would not have misheard the call sign; but ultimately I should have realized my attention had been entirely focused on the checklist; not the radio; and asked Tower for a short delay; clarification; or repeated clearance. We were operating the second leg of the day as Aircraft X from ZZZ to ZZZ1. We were given a short taxi from the terminal to Runway XXR. Approaching the departure end of XXR I switched to Tower frequency while still completing the Before Takeoff Checklist. As we made the turn from B onto B5 and while still finishing the last few steps of the checklist; Tower cleared another aircraft with a similar-sounding call sign; to line up and wait on XXC. I mistakenly thought the line up and wait clearance was for us and read back a clearance to line up and wait on Runway] XXR. Tower did not acknowledge my call; and while the Captain and I both saw an aircraft on final for [Runway] XXR; it appeared there was adequate spacing for the line up and wait clearance to be reasonable. As our aircraft passed the hold short line; Tower cleared the similar call sign for takeoff on XXC. The Captain and I simultaneously realized there had been a possible mix up of call signs. We advised tower we had read back the line up and wait clearance and asked for confirmation that it had been for us. Tower advised that it had not been for us; but cleared us for an immediate takeoff to accommodate the aircraft on final for [Runway] XXR. We immediately transitioned to a rolling takeoff and were able to get airborne before any go-around or other action was required by the aircraft on final.


Second narrative: It did not sound right to me when the Tower said to line up and wait; but after the First Officer read back the instructions and the Tower did not correct us we pressed on. Next time I am in a situation that does not feel right; I will stop what I am doing and verify the instructions before taking the runway.We were taxiing to Runway XXR in ZZZ. As we were approaching the hold short line we heard the instruction to line up and wait. The First Officer read back 'Aircraft X line up and wait XXR.' Both of us looked at final approach and saw an  aircraft on approximately a 5 mile final; I verified this with my MFD. As we turned on to the runway the Tower cleared an aircraft for takeoff that had a very similar call sign as ours. At this point; I verified our instructions to lineup and wait. Tower said that he did not clear us to line up and wait. The Controller immediately cleared us for takeoff and so we took off.


Synopsis: A320 flight crew reported runway incursion.