But it was the person missing from the group who stood out most.
Warren, who many thought would run for president herself, has so far declined to back anyone in the primary. She is also one of only six Democratic senators who has not endorsed Clinton.
Clinton's campaign said it invited the 13 female senators who have endorsed Clinton to attend tonight's event, but would not say whether or not they invited Warren. They also would not comment about Warren's absence.
"We're honored to have 13 women Senators coming together to endorse and support Hillary Clinton," Clinton spokeswoman Christina Reynolds said in a statement, "This is a sign of the broad support Clinton is receiving from women across the country who know she'll fight for us."
Warren's senate office declined to comment.
Last year, all of the female Democratic senators -- including Warren -- signed a secret letter to Clinton encouraging her to run for president. Warren later clarified that while she supports Clinton running, she had not endorsed her.
"You know, all of the women -- Democratic women, I should say, of the Senate -- urged Hillary Clinton to run, and I hope she does," Warren told ABC News' George Stephanopoulos last year when asked if she would back Clinton.
"Hillary is terrific," she replied when asked again.
No one, however, made any mention of Warren's absence during the program. "I'm not sure why she wasn't," Mikulski said coyly, "Maybe she has a cold."
She also offered her thanks and praise of her former colleagues.
"They have so much courage and smarts, the combination of grit and grace," Clinton, a former senator, said pointing to the women standing on stage behind her, "It was the honor and privilege of my life to serve with them."