Sen. Chuck Grassley (R-Iowa), 87, told colleagues on the Senate floor that he wasn't able to spend Thanksgiving with his family for the first time in his life, because of the isolation.
The return of Grassley, third in the line of presidential succession behind the vice president and speaker of the House, was welcomed by Senate Majority Leader Mitch McConnell (R-Ky.).
"I'm especially happy to welcome back our president pro tempore," McConnell said.
"We all predicted that if any member of the body had the stamina and the spirit to kick the virus to the curb, it would certainly be him. And sure enough, our colleague reports that he experienced no symptoms. His doctors have cleared him to come back to work, and we're sure glad to have him back."
In a written statement, Grassley said he was thankful for the well wishes and prayers from Iowans and Americans from other states.
"This disease affects people differently," he said. "I did not experience symptoms, but more than 1,000 Americans are dying every day and many more are hospitalized. That means we all have to do our part to help protect our friends, family, and fellow Americans. I will continue to wear a mask and practice social distancing."
A significant percentage of COVID-19 patients show no or few symptoms. A small percentage require treatment in hospitals and some die.
Symptoms include fever, aches and pains, and loss of taste and smell.
Grassley has spent 39 years in office. He won with 60 percent of the vote in the 2016 election. His current term ends in 2023.