"I say if Kamala Harris runs, she is the Democratic nominee," Coulter said during a speech Thursday evening, as quoted by Breitbart News TV editor Jeff Poor.
Harris, a former attorney general of California, has long been rumored to be considering a 2020 run, but publicly has shied away from that kind of talk.
Speculation has heated up as the former California attorney general has done some fundraising, including in the Hamptons in July.
Harris is expected to visit Florida, a key battleground state, in November to help raise money for fellow Democratic Sen. Bill Nelson.
Some fellow Democrats have also said they expect Harris to run.