Johansson is the sixth signing the Championship newcomers have made in the summer transfer window, and the second goalkeeper after the addition of Jamal Blackman on a season-long loan deal from Chelsea.
The 21-year-old started his career at Hammarby before being signed by Aston Villa, spending four seasons in their academy until moving to Leicester two years ago.
After the expiration of his contract with the Foxes, where he never made a senior appearance, Johansson has been training with the Millers and impressed manager Paul Warne enough to earn a contract.
Sweden Under-21 international Johansson, who will face competition from fellow stoppers Blackman and Lewis Price, said: "I’m delighted, it’s a great club and I’ve heard loads of good things about it, so I’m very happy to be here.
“I’m very excited, both guys (Jamal Blackman and Lewis Price) are awesome. It’s a great training group with a lot of experience, especially with Pricey who has been in the game for a very long time, I’m looking forward to working with them.
“I’d say I’m an explosive goalkeeper, quick off my line, good at shot stopping and good with my kicking.”
Rotherham’s promotion from League One last season was helped by the consistency between the posts of Dan Iversen, who was on loan from Leicester. Johansson said that his former team-mate’s experience at the club helped him make his decision to join.
“I spoke to Dan (Iversen) quite a bit last season when he was on loan here and he really enjoyed his time at the club and thought it was great here. Of course, that played a big part in me joining the club,” he added.
Boss Warne says that he knew very quickly that he wanted to sign Johansson, who had joined the club for a two-week trial.
“During the first practice game on his first day in training I told him we were going to give him a deal,” he told the Rotherham Advertiser. “I thought he was brilliant. He couldn’t stop smiling.”
Blackman is still likely to be favourite to start the season as first-choice goalkeeper, but Warne has every confidence that Johansson can develop into an important player.
“He might not be 100 per cent ready to be our number one, but in all the games he’s played in during pre-season he’s been excellent,” said Warne.
“He’s a bubble of fizz. He comes off his line, his distribution is really good. He came over from Sweden and had to spend two weeks in a hotel, which he didn't blink at.
"He wants the challenge. He understands that he's going to have to compete with Jamal. I see him as a goalkeeper who is going to be here for a few years. Hopefully he progresses under Andy (goalkeeping coach Warrington). It's a big development year for him.”
Millers building nicely
Johansson’s signing leaves the Millers well-stocked in the goalkeeping department as they prepare for their second-tier return. Warne is moving closer to completing his squad, adding to the four outfield signings already made.
Wes Harding and Angus MacDonald have both been brought in to provide more Championship experience in defence, with Rotherham paying an undisclosed fee to Birmingham City for Harding and MacDonald joining on a free from Hull City.
Harding made 60 appearances for the Blues but is still only 23, and brings utility value by being equally comfortable at centre-back or right-back, while central defender MacDonald has featured in the second-tier for both Barnsley and Hull and is on the comeback trail in his career after recovering from bowel cancer.
In attack, the Millers made the impressive capture of winger or attacking midfielder Kieran Sadlier from South Yorkshire rivals Doncaster Rovers. Although yet to play in the Championship, Sadlier arrives on a free transfer with an excellent reputation and was Doncaster’s top scorer last season with 11 league goals.
Their attacking options were also boosted by their first signing of the summer, Mickel Miller, with the wide player joining from Scottish side Hamilton Academical.
Further midfield cover would now be appear to be the top priority for Rotherham, who are building nicely and will be prepared to be patient with more than a month remaining of the transfer window.
Their season begins on Saturday with a trip to League Two side Salford City in the first round of the EFL Cup, before travelling to fellow Championship newcomers Wycombe Wanderers the following weekend to start their league campaign.