Senator Adeleke's elder brother, Isiaka, had planned to contest for the same governorship election before he died in April 2017.
Adeleke announced his plan to run for the office in a letter written to the Peoples Democratic Party (PDP).
In the letter addressed to the PDP, he said he is joining the governorship election race because he believes he possesses "all it takes to unite leaders and members of our party as well as galvanise the general electorate towards ensuring a resounding victory for the PDP in the forthcoming poll."
"In accordance with the directive of the leadership of our great party, I wish to respectfully express my intent to vie for the ticket of the party as its candidate in the Osun state governorship election holding on the 22nd September 2018," Adeleke wrote.
"I am a member of the party in Sagba Abogunde ward 2 of the Ede north local government in the Osun west senatorial district.
"As a loyal man from the strongest political base of the PDP in Osun state, I am willing, able and prepared to offer myself for this great service if given the opportunity to fly our flag as the governorship candidate.
"I pledge my continuous commitment and support to the stability, growth and success of the PDP at all levels", he added.
Adeleke had in 2017 defected from the All Progressives Congress (APC) to the PDP to contest the Osun west senatorial district election.
The seat became vacant after his elder brother, Isiaka Adeleke, who occupied it, died in April 2017.
Before his death, Isiaka planned to run for the governorship election in Osun.
Ademola is also the famous 'dancing senator' uncle of pop star Davido.