Lubanga, who led one side during fighting between two Congolese communities, was the first person to be convicted by the ICC, in 2012.
He was sentenced to 14 years for using child soldiers and raping girls.
He is eligible for release after serving two-thirds of his sentence.
He has been in custody since being arrested in the Democratic Republic of the Congo in 2005.
Lubanga told the hearing at The Hague that he wanted to return to DR Congo and pursue a doctoral thesis in the city of Kisangani, to identify a new form of sociology to help "tribal groups to live together in harmony".
He led a militia in the gold-rich Ituri region of DR Congo during a conflict between the Hema and Lendu communities, in which an estimated 50,000 people died and hundreds of thousands were made homeless.
His legal team argued that in general, "convicts are systematically  released once they have served two-thirds of their sentence" in international  justice.
Prosecutors objected to his request, saying he had been interfering with witnesses in another case linked to the conflict in DR Congo.
Lubanga denied the accusation.
The judges did not say when they would issue their decision.
Thomas Lubanga
•Leader of the Union of Congolese Patriots (UPC), an ethnic Hema militia
•Head of the UPC's military wing, the Patriotic Forces for the Liberation of Congo (FPLC)
•Accused of recruiting children under the age of 15 as soldiers
•Arrested in Kinshasa in March 2005
•Held by the ICC at The Hague since 2006
•Born in 1960, has a degree in psychology
Lubanga profile
Congolese warlord Thomas Lubanga wants to be released from prison early to study the causes of ethnic conflict, he has told the International Criminal Court (ICC) in The Hague.