Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument; Flight Crew Multiengine
Aircraft Equipment Problem Critical; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy
Air Traffic Control Provided Assistance; Flight Crew Diverted; Flight Crew Landed in Emergency Condition; General Maintenance Action
Aircraft
I was CA (Captain) and PM (Pilot Monitoring).  Departed late due to ELAC (Elevator & Aileron Computer) 1 MEL (Minimum Equipment List).  South of ZZZ at FL390; we had ECAM for HYD (Hydraulic) G RSVR (Reservoir) LO AIR PR (Low Air Pressure).  I ran the ECAM and told ATC we had a HYD issue.  ECAM put us into ATL LAW (Alternate Law) and FO (First Officer) had to hand fly.  We asked for lower altitude and told ATC we wanted ZZZ1 and I sent ACARS to Dispatch.   I was running the COM and getting ATIS and found out ZZZ was showing 002OVC (200' Overcast) and 1 1/2 vis (Visibility).  I asked ATC if there was anything better for weather and he said the region was all the same.  We decided to go to ZZZ.  Once the COM was complete I called and briefed the FA's (Flight Attendants) and made PA to the passengers.  We decided that I would take over and fly the approach and landing. We briefed the ILS 11 Approach and the FO hand flew the Aircraft until about 15-20 mile final so I could take my time and take a few minutes to 'gather my thoughts.'  We started to configure early and we had to gravity extend the gear.  Now we were in direct law and started to fly the approach..  We saw the approach lights and continued and saw the runway at minimums.  We landed.  We taxied to the gate and briefed the passengers and deplaned.  I made the phone calls to Company; Dispatch and Maintenance.  Maintenance looked at the issue and found out there was HYD fluid all over and we had a bad O ring. They fixed the issue and we were about to land in ZZZ1 about 5 hours late.
A320 Captain reported a Hydraulic System Failure inflight resulting in a diversion.