Boro will pay £1.4million for Bailey, who has agreed terms on a contract subject to a medical on Monday.
"The fans of Charlton made me very welcome from day one and I would also like to thank them for that," he told Sky Sports.
"I am extremely excited about the challenge ahead of me at Middlesbrough, as I know it is a massive club with plenty of passionate fans with high expectations."
Coventry City have agreed a deal to sign Sunderland forward Roy O'Donovan on a three-year contract.
The Irishman, 24, will link up with the Sky Blues at the beginning of July, having struggled to make his mark with the Black Cats.
Swansea City have given a three-year contract to midfielder Lee Lucas, who has come through their youth academy.
Lucas, 18, has yet to make an appearance for their senior team but was a regular in their reserve team last season and is a Wales U19 international.
Adam Pearson, the Hull City chairman, has dismissed suggestions the club are prepared to pay off top earner Jimmy Bullard.
The Tigers are seeking to cut costs following relegation from the Premier League, but Pearson has insisted they will not do that by paying Bullard to cancel his contract.
"I don't know where that story has come from as we are not in the habit of paying players off," he told the Hull Daily Mail.
"We are where we are with Jimmy. He has a contract and we have no intention of paying people off.Jimmy is available for transfer or on a season-long loan and we have had some interest but nothing further."