The sensational exit of Leonardo Bonucci to Milan earlier this summer prompted Juve to seek a new centre-back for the coming season.
And, on Wednesday, the Serie A champions confirmed that Howedes would be spending at least the next 12 months in Turin.
The 29-year-old Germany international moves on a loan deal, with Schalke receiving an initial €3 million.
If he plays 25 competitive games Juve would also be obliged to exercise his purchase option, which was agreed at €13m plus another €3m in bonuses related to clauses valid until June 2020.
Howedes joined Schalke as a trainee, and has represented the Gelsenkirchen club throughout his career.
The centre-back made a total of 334 appearances for Schalke, scoring 23 goals and helping them to the DFB Pokal title in 2010-11.
He has also picked up 44 caps for Germany, and was a cornerstone of the side that lifted the 2014 World Cup in Brazil.