The Grammy-winner appeared on stage to support Democratic presidential nominee Kamala Harris, making a short speech about the importance of freedom of speech, before introducing Obama.
"I have done a lot of rallies, so I don't usually get nervous," Obama said.
"But I was feeling some kind of way following Eminem," before he rapped the words to Lose Yourself - the theme song to Eminem's semi-autobiographical film 8 Mile.
"I thought Eminem was going to be performing, I was going to jump out," the 63-year-old joked, before adding: "Love me some Eminem."
Eminem told the rally that he was at the event "for a couple of important reasons", ahead of the 2024 presidential election next month.
"As most of you know, the city of Detroit and the whole state of Michigan mean a lot to me," the 52-year-old said.
"And going into this election, the spotlight is on us more than ever, and I think it's important to use your voice. So, I'm encouraging everybody to go out and vote please.
"I also think people shouldn't be afraid to express their opinions, and I don't think anyone wants an America where people are worried about retribution, of what people will do if you make your opinion known.
"I think Vice President Harris supports a future for this country where these freedoms and many others will be protected and upheld."
The Harris campaign has featured a host of famous faces, with singer Bruce Springsteen scheduled to appear at a rally in Atlanta on Thursday and Oscar-winner Julia Roberts campaigning for Harris in Georgia earlier this month.
-- BERNAMA
