The Massachusetts senator says he instigated the stumping for Kirk.
He's had more than 100 requests from struggling candidates to come stump for them.
But Brown, who's in town to headline a fundraiser for Mark Kirk, says Kirk didn't even have to ask.
"I asked him if I could help him, he didn't call me," Brown said in an exclusive television interview with NBCChicago. "I think that's important to note."
Why, you might ask, did Brown, who differs with Kirk on the nomination of Supreme Court Justice Elena Kagan (Brown opposed, Kirk didn't) and the financial regulation bill (Brown is for it, Kirk is against it) want to come and help out?
"(Washington needs people) regardless of party, quite frankly, who are good people, are good workers in the interests of their citizens," Brown said. He adds: "[Kirk's] going to be bombarded by the unions, the special interests, [and the] President's going to come to out to do what he can to retain that seat."
Brown says that he and Kirk are simpatico on the things that count, like working from the middle and not taking a hard line on their party directives. He said he and Kirk could be among the Republican senators who reach out to Democrats instead of getting caught up in filibusters and majorities.
As far as Kirk's verbal missteps, Brown says he thinks the voters will forgive and forget.
"I don't know too many perfect people in this world," said Brown, who like Kirk served in the National Guard.
Brown is expected to help raise close to $200,000 while he's in town.