NATO invited Zardari to the conference, which is set for next Sunday and Monday, Tuesday, several days after Anders Fogh Rasmussen, the military alliance's secretary-general, suggested Pakistan wouldn't be invited because it still blocked NATO supply routes to neighboring Afghanistan, CNN reported.
Relations have been strained between NATO and Pakistan since NATO airstrikes killed two dozen Pakistani soldiers in November. Pakistan closed the supply route to Afghanistan in response.
The decision to attend the Chicago meeting was made after Zardari consulted with Pakistan's top military and civilian leaders, the statement said.
Talks to reopen the border have heated up in the run-up to the Chicago summit. U.S. negotiators have been in Pakistan since late April. Last weekend, Gen. John Allen, who oversees U.S. and NATO troops in Afghanistan, and his Afghan counterpart met in Pakistan to discuss the border issue, among other things.
Analysts said the NATO summit invitation was an incentive for Zardari to reopen the supply routes, CNN said.
Zardari spokesman Farhatullah Babar said Tuesday the invitation was unconditional and not tied to opening ground lines of communication for NATO or to any other issue.
Zardari is scheduled to speak in Chicago and have several side meetings with international leaders, his office said.