Shadow chancellor John McDonnell accused the Government of "betraying" students as he addressed crowds at a demonstration backing free education.
Labour leader Jeremy Corbyn also threw his support behind the protesters by demanding the abolition of tuition fees in a statement read out at the rally.
Thousands of students braved the rain to attend the demonstration in central London, which is calling for the end of fees, the return of maintenance grants and an end to student debt.
Mr McDonnell was greeted with cheers as he climbed up a small platform to address the students through a megaphone.
He said: "Your generation has been betrayed by this Government in increases to tuition fees, in scrapping the education maintenance allowance and cuts in education.
"Education is a gift from one generation to another, it is not a commodity to be bought and sold.
"For generations now, one generation has handed the baton to the next, they have tried to ensure that the next generation has a better quality of life than the last.
"This Government is betraying you and future generations. You need to oppose it and I'm here in solidarity with that opposition."
As students waving placards cheered, Mr McDonnell said education is "a basic human right" that must be protected.
Mr Corbyn did not attend the rally but sent a message of support which was read out.
In it he reiterated his proposals to scrap tuition fees and restore the education maintenance grant and urged students to "keep protesting, keep campaigning for justice".
He added: "Education is a right, not a privilege."
Mr Corbyn said there is an "opportunity to change course and to change Labour into a force that represents students' desire for free and accessible education".
The march is challenging plans to scrap maintenance grants and replace them with loans, which critics warn will plunge the poorest students into thousands of pounds of extra debt.
At present, full-time UK students from families with annual household incomes of £25,000 or less qualify for maintenance grants of £3,387 a year, with smaller amounts awarded according to income.
But under the changes, which come into force in the next academic year, these grants will be replaced by loans which students would start paying back when they earn more than £21,000 a year.
Mr Corbyn warned this would "push the poorest students into higher levels of debt".
A spokesman for the Department for Business, Innovation and Skills said: "This Government is committed to ensuring everyone with the potential to benefit from higher education has the opportunity to do so, regardless of their background.
"It has always been the case that student support provided by government is a contribution to living costs and institutions themselves offer a range of bursaries, scholarships and grants.
"Our system means that lack of finance should not be a barrier to participation and more funding is available to support living costs than ever before."