As the fourth presenter of the programme since it began in 1962, the Co Down man made history on Friday.
To witness Kielty make his debut, viewers from all around the world tuned in to a show that also featured Tommy Tiernan, former president Mary McAleese, and football player James McClean.
RTE said on Monday that the programme averaged 830,000 viewers on RTÉ One and RTÉ One +1, with a 62% audience share.
The show on Friday night had a peak audience of 934,000 viewers and 158,000 streams on RTÉ Player, making it the strongest Late Late Show debut on that platform.
Adults ages 25 to 44 accounted for 65% of the audience.
Since September 1, footage from the Late Late Show have received 7.6 million views on social media.
Kielty, 52, takes over as host of the Late Late Show after Ryan Tubridy. The beginning of this year, Tubridy resigned.
When RTÉ admitted it had not accurately revealed Tubridy's fees between 2017 and 2022, when he was the highest-paid presenter, he found himself at the centre of the crisis after leaving the programme.
As further information concerning RTÉ's internal financial, accounting, and governance practises as well as its spending on corporate hospitality for advertising clients came to light, the controversy surrounding the payments expanded to become a larger crisis for the national broadcaster.