Maddow was absent from her show for around two weeks after disclosing that she had been in close contact with someone who tested positive for the infection.
Returning to the air on Thursday evening, Maddow said that person was her partner of 21 years, Susan Mikula.
“At one point, we really thought it was a possibility it might kill her and that’s why I’ve been away,” Maddow said.
Maddow said her partner, who she described as "the centre of my life", is recovering well.
Maddow said she had tested negative for coronvirus herself and delivered Thursday's show from her New York home, where she is self-isolating.
She hosts The Rachel Maddow Show, MSNBC's most-watched current affairs programme, which has been running for more than a decade.
In a plea to her viewers, Maddow called on the public to take the virus seriously.
"Don’t get this thing. Do whatever you can to keep from getting it," she said. "For Thanksgiving next week, you really are just going to have it at home without people coming over.
"Yeah that's going to suck, but it's going to suck so much less than you or someone in your family getting sick. Trust me," Maddow added.
Coronavirus infections continue to surge in the US. Health officials reported 187,396 new cases on 19 November, according to official data.
Some 5,000 of those infections were recorded in Maddow's home city of New York, where 24,000 people have died from the disease.
Country-wide, more than 250,000 people have died after contracting the infection.
Additional reporting by Associated Press