Adeleke polled a total of 97,480 votes, to defeat Hussain of the All Progressives Congress (APC) who secured 66,116 votes. Adeleke won nine out of the 10 local government areas where the election held.
Aregbesola had personally led the campaign for Hussain, touring all the local government areas with him.
However, he has conceded defeat and says "it is a victory for democracy".
The Governor wrote on his official Twitter account: "I congratulate Ademola Adeleke on his victory at the polls yesterday.The people have spoken. Democracy won and we respect the people's choice.
"I thank our supporters for their continued show of commitment to our cause. Important lessons have been learnt and we will be back stronger.
"Most importantly, I thank the people of Osun for once again displaying the qualities of true Omoluabis. Our election was devoid of violence."