The actor and director is an outspoken conservative in Hollywood, and came forward at the Florida convention to show his support for Republican presidential candidate Mitt Romney.
In his speech, the 82-year-old criticised incumbent president Barack Obama's policies concerning health care and the economy.
He said of Obama's election in 2008: "Oprah was crying. I was even crying. I haven't cried that hard since I found out that there's 23 million unemployed people in this country.
"That is something to cry for. It may be time for somone else to come along and solve the problem."
Eastwood conducted the speech as a debate, turning to an empty chair and addressing it as if it were the absent Obama.
At one point in the address he said to the chair: "I'm not gonna shut up," and later added, "What? What do you want me to tell Romney? I can't tell him to do that to himself. You're absolutely crazy."
Eastwood's appearance at the Republican rally was rumoured earlier on Thursday, when a source revealed that the veteran actor would be attending the event.