In an interview with CNN on Wednesday morning, Reid detailed Clinton's accomplishments as first lady and later as a senator from New York.
"I think that my work with her over the years has been something that I have looked upon with awe. She was the first lady. She started the trend toward looking to do something about health care. She understood the issue well, she was the front on the health care during that administration," he said. "I also think she's the woman to be the first president of the United states that's a female."
Reid is the highest ranking Democrat to throw support behind Clinton, adding to the veritable pile of Senate and House endorsements she's raked in.
Clinton won the Democratic caucuses in Reid's home state of Nevada on Saturday, and is projected to beat Sen. Bernie Sanders, D-Vt., in South Carolina's Democratic primary this Saturday.
Reid, who said he's had a close relationship with Sanders over the years, said he had called Sanders to break the news to him on Tuesday.
"It was a really wonderful call," Reid said, calling Sanders "so magnanimous, so kind and courteous."
Reid is a superdelegate, meaning he's yet another nomination vote in favor of Clinton, further widening the chasm between her and Sanders when it comes to pledged support from superdelegates. Clinton now has 452 superdelegates to Sanders' 19.