The Herald can reveal that the debut episode of McWilliams' first outing as host of the satirical show on Thursday drew in an average of 282,000 viewers.
The viewing figures represent an average audience share of 23pc, a significantly smaller figure than a number of other top-rated shows on television.
Among the programmes topping the ratings are TV3's The Apprentice, with 451,000 viewers tuning in last Monday, and Pat Kenny's current affair's show Frontline, which recorded 343,000 viewers that week.
Just days before his new programme went to air, McWilliams hit the headlines for all the wrong reasons.
It emerged that his new book Follow the Money contained remarks about Prime Time presenter Miriam O'Callaghan, which were perceived to be sexist by many.
One line in the book reads: "Miriam winks, with a faint pout and the casual lick of those hyper-glossed lips. You're mine now, boy, she signals. This is my web you've just walked into. Clothes on or off."
He went on to compare the mum-of-eight to "Hannah Montana's ma".
Having dominated the headlines for days, McWilliams used the first episode of The Panel to issue a grovelling apology to O'Callaghan.
McWilliams was criticised by O'Callaghan over the comments, as well as by a series of high-profile journalists, including Today FM presenter Matt Cooper.
Even Finance Minister Brian Lenihan was said to be annoyed by references to their personal friendship.
McWilliams said: "I really like [O'Callaghan] and we get on well together. I screwed up.
"The whole thing has been a disaster for me and for her."
On hearing of his comments, O'Callaghan said she was "very happy" to accept the apology and even wished McWilliams the best of luck with the show.