Many Republicans had argued that the trial should not go ahead at all, claiming it was unconstitutional to try a president who is no longer in office. However, the Senate allowed the trial to go ahead after six Republicans joined all Democrats in a 56-44 vote.
Jamie Raskin, a Democrat and lead impeachment manager, addressed those present as he introduced the jarring footage.
He said: “You will not be hearing extended lectures from me, because our case is based on cold, hard facts.”
The clip shows Mr Trump addressing cheering supporters with statements such as “we will stop the steal” and “you can’t vote on fraud”.
After the video had played, Mr Raskin said: “Senators, the President was impeached by the US House of Representatives on January 13 for doing that.”
According to Sky News, Mr Trump’s second impeachment trial is due to last into the middle of next week.
Analysts have said it is not likely that enough Republican senators will vote against Mr Trump in the final vote.
Prior to yesterday’s trial proceedings, Mr Trump’s lawyers had said the trial could not go ahead on the basis that Mr Trump had already left office.
His colleague David Schoen claimed the trial would “open up more wounds across the nation”.