Bundesliga strugglers Borussia Dortmund have agreed to sign Slovenia international Kevin Kampl in January.
Cardiff have agreed to sell Norwegian midfielder Mats Daehli to Freiburg in January.
The 22-year-old has signed a four-year contract with the SPL champions having been targeted as one of Neil Lennon's top summer targets.
Balde's arrival will likely lead to questions about the future of Hull City target Gary Hooper but he is delighted to have arrived after being won over by Celtic Park's unique atmosphere.
Speaking to Celtic TV, Balde said: "I am very happy to sign my contract with Celtic.
"I'm proud to sign for Celtic and want to do everything I can to take this opportunity, work hard and grow as a player.
"I fell in love with the club three years ago and I watched every game on TV."
"When I saw the Barcelona game last year [in the Champions League] it was crazy and I loved the crowd.
"After watching that game, there are no words I can say to describe what it will mean for me to play for Celtic."