Maryland Sen. Barbara Mikulski nominated Hillary Clinton, who has the delegates needed to win in the roll call vote to follow.
Mikulski delivered speech on behalf of "all women who have broken down barriers for others."
Mikulski was the first Democratic woman to be elected to the Senate in her own right.
A Hawaii congresswoman nominated Bernie Sanders for president.
In response to the move by Tulsi Gabbard, Sanders' delegates jumped to their feet in applause.
Gabbard was one of Sanders' major backers during his primary campaign.
She calls the Vermont senator's campaign "a movement of love," and says "it can never be stopped or defeated."