The former Take That singer revealed last month that he would be bringing his Swings Both Ways tour to Glasgow's newest venue on Thursday, June 26 2014.
He will now also play the venue on Friday, June 27 2014.
Williams scored the 1000th UK number one album last month when his new record, Swings Both Ways, topped the charts.
Tickets for both Hydro shows will go on sale at 9am on Friday, December 6. Prices range from £55 to £70.