More than half of the Welsh population watched the Gavin & Stacey finale on Christmas Day.
The BBC's director-general, Tim Davie, announced the record-breaking figures for the show at an event for industry leaders in Cardiff.
He said: "Nothing demonstrates the BBC’s ability to bring people together like the extraordinary success of Gavin & Stacey."
The figures show that 1.8 million people in Wales, or 59 per cent of the Welsh population, have watched Gavin & Stacey: The Finale.
This makes it the most-watched TV moment in Wales since at least 2002, surpassing the 2012 Olympics opening ceremony peak of 1.4 million.
The statistics also reveal that people in Wales are twice as likely as the rest of the UK to have watched the finale at least twice.
Across the UK, 2.8 million have watched the Christmas Day episode more than once, equivalent to four per cent of the UK population.
In Wales, the corresponding figure is 245,000, equivalent to eight per cent of the Welsh population.
People in Barry and the surrounding areas (CF postcode) are 29 per cent more likely to have watched the finale on BBC iPlayer.
The figures also show that Gavin & Stacey: A Fond Farewell is the best-performing single BBC Wales programme on record, with 8.7 million views across the UK.
BBC Cymru Wales commissioned the emotional documentary, which featured many of the cast and some of the series’ die-hard fans as they looked back on 14 years of the beloved show.
Rhuanedd Richards, director of BBC Cymru Wales, said: "I’m incredibly proud to see the success of Gavin & Stacey, The Finale and our documentary, both across the UK and with the record-breaking numbers here in Wales.
"Over its 17 years on our screens, Gavin & Stacey, which is so synonymous with Wales, has become one of the most beloved sitcoms of all time.
"It’s a programme that we as a nation feel so strongly connected to, and these figures certainly reflect that."
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