Manager Paul Jewell moved quickly to snap up the 34-year-old after Wanderers announced last week they were releasing him after nearly eight years with the club.
He is keen to have more experience in midfield next season, and with more than 500 senior games under his belt –including 22 international caps – Frandsen fits the bill.
The player underwent a medical in Wigan yesterday after flying in from Denmark, and will report back for training with his new team-mates at the beginning of July.
Jewell is pleased to have completed his first piece of transfer business so early in the summer.
And once he returns from holiday, he hopes to make a further three or four signings to bolster the squad.
Jewell told the Evening Post: "We've done a deal to sign Per Frandsen on July 1 when his contract at Bolton runs out.
"When I heard last week they were releasing him, I knew there would be loads of clubs in for him so I had to move quickly.
"I put plenty of feelers out and I already knew plenty about him as I tried to sign him when I was Bradford manager.
"Sam Allardyce at Bolton can't speak highly enough of him and he played 38 games in a successful side last season.
"Per is tried and trusted, and okay he might be 34, but his fitness is still of the highest standard.
"Teddy Sheringham is still going at 38 and Stuart McCall at 40, and as long as they look after themselves, players can keep going for a long while.
"Last season our midfield was full of energy and enthusiasm with Jimmy Bullard and Jason Jarrett who did a great job for us.
"But sometimes we lacked an experienced holding player in there, a bit of knowledge if you like.
"Per will give us that, while Jimmy and Jason will have benefited from a season in Division One."
Latics beat off competition from Premiership newcomers Norwich City to sign Frandsen, and there was also interest from clubs in Denmark.
Jewell said: "It was actually a very easy deal to do as Per lives in the Bolton area and his kids go to school there.
"He had watched some of our games this season and was very impressed with what he had seen.
"He sees us as an up and coming club and it was good to hear him talk the way he did about us."
Frandsen kicked off his career with home town club B1903 Copenhagen and then spent four years in French football with Lille before returning to Denmark to play for FC Copenhagen.
In the summer of 1996 he joined Bolton for £1.25m, making 129 appearances, before moving to Blackburn three years later.
But his stay at Ewood Park lasted less than a year, and he returned to Wanderers in July 2000, going on to play a further 116 league games.
He played the majority of their games in the season just ended as the Trotters secured their highest ever Premiership placing of eighth.
