Flight Crew Air Transport Pilot (ATP); Flight Crew Multiengine; Flight Crew Instrument
Flight Crew Last 90 Days 177; Flight Crew Total 5143; Flight Crew Type 4028
Situational Awareness; Communication Breakdown; Confusion; Time Pressure; Distraction
ATC Issue All Types; Conflict Ground Conflict; Critical
Flight Crew Took Evasive Action
Environment - Non Weather Related; Human Factors
After landing on Runway XXR in ZZZ; upon clearing the runway we were told via ground to taxi north on Taxiway 1 and enter the ramp at Taxiway 2 for parking at the Gate X. I was the FO acting as an LCA. Both ZZZ ground and ZZZ X concourse ramp frequencies were completely saturated with traffic both inbound and outbound. Upon making the left 90 degree turn onto Taxiway 2; I noticed a rapidly approaching taxi light of an aircraft northbound on Taxiway 3. I immediately directed the Captain to stop and I also abruptly braked from the right seat. Aircraft Y continued to taxi right in front of us and then stopped short of Gate Y to give way to an outbound aircraft. We were never notified by Ground of a potential conflict or to give way to the northbound aircraft. We subsequently were cleared by ramp onto the ramp and to our gate. We missed the other aircraft by about 50 feet.
Taxiing north on Taxiway 1 with a Taxiway 2 entry to ramp for the Gate X.   Cleared Taxiway 2 to entry but not cleared to enter ramp. I made left turn on Taxiway 2 was prepared to stop at Spot XX.  Captain was monitoring ground on VHF1 and Ramp on VHF2.  I was only monitoring Ground on VHF1. I started the turn and was about to cross Taxiway 3 when LCA Captain in right seat  yelled 'STOP STOP STOP!'  I applied immediate max braking and abruptly stopped the aircraft.What I did not see was another taxiing aircraft from my left on Taxiway 3. I was given no radio call to give way to that traffic. My clearance was to the ramp. I do not know why I did not see the approaching aircraft. It was dark and their taxi light was not pointed at me. Regardless; I should have seen it.   We stopped and I would guess our nose was within 50 feet of their wingtip.  I do not know if they saw us or not.  No comment from Ground or ramp about what just transpired.I will say that fatigue may have been an issue.  This was an OE after a 6+ month break in flying and I was feeling some mental fatigue.
Air carrier flight crew reported a ground conflict. The Captain stated fatigue and months without flying contributed to the event.