The co-stars led the crowd in a chant of VP Kamala Harris' campaign slogan: "When we fight, we win!"
Harris is expected to accept the nomination for the Democratic ticket.
Democratic delegates turned up and broke it down thanks to DJ Cassidy!
Colbert also questioned Pelosi about Palestine, noting that her answer appeared "unsatisfying to some people."
This isn't the first appearance Walz has made at the DNC.
The former president and first lady are both scheduled to speak on Tuesday night.
The president is expected to take the podium on Monday night.