"I think it may be time for somebody else to come along and solve the problems," he said to loud applause.
His stand-in for the "attorney," President Obama, was an empty chair on stage that he addressed in a mock interview -- a performance both awkward and uproarious, while being perfectly Clint.
At one point, he suggested the chair-Obama had told him to "shut up."
Eastwood's appearance before Mitt Romney's speech accepting the GOP presidential nomination capped days of buzz about the convention's "mystery guest." The secret was out by the time Eastwood strolled onto the stage to huge applause.
"Save a little for Mitt," Eastwood said, before declaring, "I wasn't a big supporter" of Obama.
The star of "Dirty Harry" and a two-time Oscar-winning director jokingly said he -- like Oprah Winfrey and other Americans -- wept with joy when Obama was elected in 2008. He then turned serious, saying he wept harder at the realization 23 million people are unemployed in the United States.
Eastwood, seemingly speaking off-the-cuff, quickly tried to knock down the criticism that somebody from "left-wing Hollywood" could back a GOP presidential candidate, saying Hollywood conservatives may not "go around hot-dogging, but believe me, they are there."
The 82-year-old actor was critical of Obama's war in Afghanistan, saying he should have considered that Russia fought unsuccessfully there for 10 years.
And of course, it wasn't too hard for the audience to persuade him to deliver his signature line: "Go ahead, make my day," he said, with the crowd joining in.
Twitter was instantly ablaze with reaction.
Minutes after Eastwood began his speech, someone created the @InvisibleObama account on Twitter. It already has 17,000 followers and counting.
"Clint Eastwood is now backstage arguing with a vending machine," joked Canadian comedian Daryn Jones.
Film critic Roger Ebert didn't give the speech two thumbs up.
"Clint, my hero, is coming across as sad and pathetic," tweeted Ebert. "He didn't need to do this to himself. It's unworthy of him."
Comedian Roseanne Barr put it simply: "clint eastwood is CRAY" -- a slang reference to being crazy.
Not everyone agreed.
"Clint Eastwood made my day," tweeted Southern rocker Charlie Daniels. The Hollywood trades gave it positive marks, perhaps a reflection of the movie world's appreciation for genuineness.
Eastwood, a fiscal conservative who leans left on social issues, has confounded the political world. He starred in Chrysler's "It's Halftime in America" Super Bowl ad earlier this year even though he opposes government bailouts. The commercial angered conservatives.