Liam Burns, who was previously the leader in Scotland, was heckled and forced from the stage at the event in Kennington Park.
Students, including more than 1000 from north of the Border, took part in the central London event.
Chants of "NUS, shame on you" could be heard as Mr Burns went on stage to call for peace. The demonstration ended in farce when a band of about 20 activists climbed on to the stage.
The rally was over education cuts, tuition fees and austerity measures.
One of the protesters grabbed the microphone and attempted to address the crowd, but the microphone was cut. Mr Burns said: "When people say that we are not united in picking the right fights, fighting the real enemies in Government rather than among ourselves. Well, witness it here."
President of NUS Scotland Robin Parker said: "There are a whole range of issues where what the Westminster Government are doing is having a terrible effect on Scotland. On economic policy and its impact on youth unemployment. On tuition fees in England, where we now have English students in Scotland paying up to £36,000 a year."