"We face a challenging new security environment, including hybrid warfare, cyberattacks, the threat of terrorism. US leadership is as important as ever," Stoltenberg said.
"I look forward to working with President-elect Trump," he added.
Trump caused consternation during the campaign when he suggested Washington would think twice about coming to the aid of an endangered NATO ally if it had not paid its dues, casting doubt on the US-led alliance's core collective defense commitment.
Asked about these remarks, Stoltenberg said "all allies have made a solemn commitment to defend each other, this is absolute and unconditioned."
"These security guarantees are important for Europe but they are also important for the United States," he said, AFP reported.
He recalled that the only time NATO's "all for one, one for all" defense guarantee has been invoked was after the 9/11 attacks on the United States.
"Our alliance has brought together America's closest friends in times of peace and of conflict for almost 70 years. A strong NATO is good for the United States and good for Europe," he said.