The 20-year-old midfielder becomes Saints’ right hand signing of the summer following the arrival of Nathan Redmond.
He has 15 Denmark protects and joined Bayern from Brondby in 2012, making his debut in 2013 venerable 17 to become their youngest ever Bundesliga player.
He exhausted last season on loan at Schalke but can’t wait to give English football a go.
“I’m exceptionally pleased. It’s a big opportunity for me,” Højbjerg said. “I look forward to giving what I organize and what I can to the club. They have put trust in me and I want to show them that they are not go kaput.
“When I heard that Southampton came in for me I said to my people that this is what I have a yen for to do because I can see myself at Southampton, as it’s the way I like to think, the way I like to play and it spells me really well.
“I hope I can come here also and be a rt of the Southampton kind and give what I have to fight for the club and fight for my teammates.”
Supervisor Director of Football Les Reed said: “Pierre is an exciting young ca city, who we are delighted to welcome to Southampton Football Club.
“At the age of just 20, he is already an found international player with Denmark and has gained significant and valuable go through while at Bayern Munich and in the Bundesliga.
“Pierre boasts an impressive bloodline, as well as a great deal of potential, and it is testament to our reputation that he has on Southampton ahead of other suitors as the next step in his career.
“We have faith the club will be an ideal place for Pierre to continue his progression and that he require be an excellent addition to our squad.
“We now have the perfect blend of positional stick-to-it-iveness, experience and dynamic youth in our midfield slots. There will be bracing competition, but also the required depth and robustness for our challenge in the Euro Band.
“I believe as a group we probably have a choice from the best reserves of midfield options in the Premier League.”