Filmmaker Spike Lee won the Best Adapted Screenplay Oscar at the 91st Academy Awards for undercover drama "BlackKklansman" and used the platform to urge people to be on "the right side of the history" in next year's presidential elections.

It was Lee's first non-honorary Oscar award as the filmmaker was conferred with an Academy Honorary Award for his contribution to cinema.

The filmmaker, who dropped an expletive right at the beginning of his speech, made a reference to Black History Month and his enslaved ancestors, who rose to prominence despite hardships.

"Four hundred years (ago), our ancestors were stolen from Mother Africa and brought to Jamestown, Virginia, enslaved. Our ancestors worked the land from can't see in the morning to can't see at night," he said in the speech.

Lee remembered to his grandmother, Zimmie Shelton Reatha for giving education a priority despite racial oppression that she and her ancestors faced.

"Before the world tonight, I give praise for our ancestors who helped build this country and today along with the genocide of its native people. If we all connect with our ancestors, we will have love, wisdom, we will regain our humanity. It will be a powerful moment.

He also urged people to make a moral choice between "love and hate" in the 2020 presidential elections.

"The 2020 presidential election is around the corner. Let's all mobilize. Let's all be on the right side of history. Make the moral choice between love versus hate. Let's do the right thing! You know I had to get that in there!" he said, hinting at President Donald Trump's controversial term.

"BlackKklansman" follows the real-life story of Ron Stallworth (played by John David Washington), a detective in Colorado Springs, who infiltrates the local chapter of a hate group and becomes the head of the chapter.

In the Best Adapted Screenplay category, the 61-year-old director was nominated alongside his collaborators Charlie Wachtel, David Rabinowitz, and Kevin Willmott.

Other nominees in the category were "The Ballad of Buster Scruggs", Can You Ever Forgive Me?", "If Beale Street Could Talk" and "A Star is Born".

He was presented the award by "Captain Marvel" stars Brie Larson and Samuel L Jackson.

Jackson, who has collaborated with Lee in the past in films such as “Do the Right Thing”  and "School Daze", looked visibly elated as he read the names on the envelop, saying "Boom!".

Lee reciprocated the love by jumping straight into Jackson's lap and giving him a bear hug as he arrived on the stage.

The director praised his family before moving the focus on to the coming US presidential election.

"The 2020 presidential election is around the corner. Let's all mobilize. Let's all be on the right side of history. Make the moral choice between love vs. Hate. Let's do the right thing! You Know I had to get that in there," he said.

Lee is up for another two Oscars -- Best Picture and Best Director.

At the red carpet, the filmmaker honoured his 1989 cult classic film "Do the Right Thing" by wearing four-fingered LOVE and HATE rings.

Lee paid tribute to the late music legend Prince with an all-purple suit and custom-made necklace donning the symbol Prince adopted as his name.