Mandzukic, 33, won four Serie A titles and three Coppa Italias, as well as scoring in the 2017 Champions League final as they lost 4-1 to Real Madrid.
He has not played this season under Maurizio Sarri and was linked with Manchester United in the summer.
“The last few months will not change the respect and love I feel for the club,” said Mandzukic.
“It has been a privilege to play for Juventus. I have always tried to do my best for the Bianconeri. I wish you the best. And for me, it’s time for a new chapter.”
Mandzukic has joined Al-Duhail on a free transfer. They are managed by Jose Mourinho’s former assistant Rui Faria and sit four points clear at the top of the Qatar Stars League.
