Commercial Fixed Wing
Air Traffic Control Fully Certified
Air Traffic Control Time Certified In Pos 1 (yrs) 3.5
Ground Excursion Runway
Air Traffic Control Provided Assistance; Flight Crew Regained Aircraft Control
Environment - Non Weather Related; Aircraft; Weather
I was working Local 2 and Ground Control combined during slow traffic and the airport was in a North flow deice configuration.  The aircraft were landing XXL with med-good braking action reports from pilots.  Aircraft X was given a clearance to land with a med-good braking action report.  Aircraft X rolled quickly pass to high speeds so I figured he was trying to roll to the end quickly.  I instructed Aircraft X to turn left at the end.  At that point he was approaching the end at a good rate of speed.  I sent the next aircraft around as I watched Aircraft X go slightly passed the end of the runway; make a hard left turn back onto taxiway M from M10 taxiway.  Aircraft X verified that he was off of runway XXL so L let the next aircraft continue and land without any issues.  Aircraft X asked to have airport vehicle to check his aircraft in case he had hit any taxiway lights.  The airport closed runway XXL.  I later observed Aircraft X taxi back to the gate on his own power.Other aircraft seemed to be able to make the high speed taxiways without any issue.  Maybe if the pilot came in with a slower approach speed it could have helped him not to roll long and slide.
Completed all briefings prior to approach. We were expecting a VFR approach but briefed like full IFR approach and were prepared for the weather to change. We were preparing for a normal approach and landing to Runway XXL. ATIS Bravo showed three miles and overcast 4100 feet. ATIS BRAVO also advised RCC CODE 5-5-5 for Runways XXR; XXL; XYL. Planned a flap 15 landing. We used conservative number of CODE 4 RCC giving us Autobrakes 2; 1530 stopping margin. In essence 3000 feet; touchdown zone being the most restrictive of the 12;000 foot runway. On final approach;  Tower stated Braking Action Good to RJ in front of us.We landing uneventfully. I believe we landed within 3;000 TDZE; however; I do remember floating a little with 10 knots ice additive. We did not have any markings visible outside center line do to white snow. Decelerated to 60 knots; F/O called 60 knots. I stowed the thrust reversers and pressed brakes to disconnect autobrakes. Nothing seemed unusual at that point. Deceleration rate seemed normal up to that point. Tower stated: 'Roll to end; aircraft behind you two-mile final.'I depressed brakes to further decelerate and realized there was zero braking available. I stated 'No brakes' to F/O a couple of times. F/O immediately told Tower and aircraft behind us went around. I extended full reverse thrust again to try and get aircraft stopped. We drifted about 45 degrees toward intended exit. We never left hard surface of runway/taxiway. I briefed F/O to contact Ground immediately and notify 'NILL BRAKING LAST THIRD OF RUNWAY XXL.'I also had F/O ask for inspection of runway/taxiway lights to make sure aircraft had no damage before we taxied any further. He also notified Company Ops what had just occurred. I briefed what had happened to Passengers on PA. ZZZ Ground Ops notified there were no runway/taxiway lights damaged. We taxied aircraft to gate without any further issues. Maintenance was waiting for us at gate and we described what had occurred. They inspected aircraft and found an actual blue taxiway light laying on top of wheel carriage on right main. There was no aircraft damage noted by the Maintenance inspection. I put a note in logbook and we deadheaded to ZZZ1.I take briefings very seriously. This was not the type of flight that either Pilot was out of loop or just not having a bad day. We were configured at the marker and on speed the whole time on approach. I may have floated a little do to 10 knot increase of VREF. The ATIS reports from ZZZ were RCC 5-5-5. The two previous aircraft reports BRAG. The only difference was; the two previous aircraft exited 2nd high speed. We rolled past the second high speed for passenger comfort. We never expected NIL braking under light snow covered runway in front of us. The airport needs to actually test the runway; if they're going to advertise 5-GOOD. It was one of the worst feelings a Pilot can have realizing he/she has lost effective control of an aircraft. Had I not redeployed the thrust reversers; I believe we would have encountered aircraft damage and maybe even injuries even though aircraft would have been exiting hard surface at a slow speed. I am actually shocked the runway had not been prepared for arrivals with so much equipment and men available at that airport. Very disappointed.
Local/Ground Controller and both pilots reported a runway excursion due to NIL braking action by the landing aircraft.