The 6ft 7in forward is the Addicks’ second new recruit this week following the acquisition of midfielder El Hadji Ba from Sunderland on a three-year deal.
Makienok began his career with Danish first division side HB Køge, scoring 22 goals in 54 league appearances before a move to Brondby IF in 2012.
A spell of 35 goals in 74 league games secured international recognition in March 2013 and a move to Palermo last September.
Makienok, 24, is set to become the tallest player to have every appeared for the Addicks’ first-team and will wear the number nine shirt during his time at The Valley.
“We now have a player who finally fills that number nine position we have been searching for,” said manager Guy Luzon.
“He will make us stronger in attack and his height will give us a very different threat which defenders will find difficult to play against, but he is very good with his feet, also.
“I’m very pleased to welcome him to Charlton and to continue building my team for the Championship.”
Makienok has won six international caps to date and is yet to find the net for his country.