McCain says he feels very good about the North Shore congressman's chances against Democratic State Treasurer Alexi Giannoulias in November.
The Arizona senator noted that Kirk is a Naval Reserve intelligence officer with the rank of commander.
"We are in two wars," said McCain. "Mark Kirk brings a degree of knowledge and background on military and national security issues that are badly needed in the leadership of this country."
A Kirk Senate victory in strongly Democratic Illinois would be doubly sweet for Republicans because the seat was previously held by President Barack Obama.
