The 23-year-old has brought a 13-year long association with the Black Cats to an end, having struggled to secure regular football over the last 12 months due to injury and then the form of Dennis Cirkin.
"I’m delighted to be here," Hume said.
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"We’ve got the deal over the line and now I’m looking to kick on.
“I first heard of the interest a couple of weeks ago, although you don’t know how concrete that is and just carry on as normal.
“It started to get stronger and then I spoke to the manager for the first time last week. He expressed that he wanted me here and my mind was made up from that point.
“I was at Sunderland for a long time and have a lot of good memories after coming up through the academy, but I think this is a good opportunity to get back to play and enjoying my football.
“You can’t really get much different in terms of going from that far north to this far south! It’s a big step, but I think the change will be good for me.
“That can really help me focus and get down to the main thing – which is obviously playing football games.
“I’ve appeared at Fratton Park for the away side and it’s a hard place to go," he added.
"It’s a ground you don’t look forward to visiting. To be there as a home player, though, is something I’m looking forward to.
“I’ll always give 100 per cent for the shirt and do everything to help this club be successful. We want to win as many games as possible this season.
"A lot of my career has been spent as a left wing-back or left-back. The first thing is to defend, but I also like to get forward and help the team score goals.”
Hume will be in contention to make his debut when Charlton Athletic visit Fratton Park on Monday night.