The former New Jersey governor confirmed his diagnosis in a tweet on Saturday morning.
Christie later said he checked himself into a hospital in Morristown, N.J., in consultation with his doctors.
“While I am feeling good and only have mild symptoms, due to my history of asthma we decided this is an important precautionary measure,” he said.
Christie added that he was “thankful for our hardworking medical professionals” and looked forward to returning home.
He is one of several prominent Republicans tied to U.S. President Donald Trump who have tested positive in recent days.
Christie was on the team that helped Trump prepare for the presidential debate in Cleveland on Tuesday.
Trump, who was diagnosed early Friday, is currently receiving treatment at a military hospital as a precaution.
His doctor Sean Conley told reporters Saturday morning the president is doing “very well” and no longer has a fever.
That account was immediately contradicted by a person familiar with Trump’s condition, who said the president was administered supplemental oxygen on Friday at the White House.
As well, Trump’s chief of staff, Mark Meadows, said the president went through a “very concerning” period Friday and the next 48 hours will be critical in terms of his care.
The circumstances in which Trump caught the virus are not yet clear. His positive test result came after staff member Hope Hicks was diagnosed with COVID-19.
Several others who travelled with Trump or attended events with the president have contracted the virus over the last several days.
Those who have tested positive include First Lady Melania Trump, former Trump adviser Kellyanne Conway, campaign manager Bill Stepien, senators Mike Lee and Thom Tillis, Notre Dame University President John Jenkins and three White House journalists.
—With files from The Associated PressView link »