He added that much work came ahead of it and much more still follows it.
"There's no question that this university's integration marked a significant moment and a tangible step forward in the long march for civil rights," said Holder, who was the keynote speaker for the Sally McDonnell Barksdale Honors College's Fall Convocation.
"It was a time of difficulty and danger for those who stood up and spoke out against the unjust status quo," he said. "It was also a moment of hope and significant promise."
Holder noted that Ole Miss had been painfully involved in history.
"Through it all, this remarkable institution has consistently served as a meeting ground for critical debates, a proving ground for innovative solutions and a training ground for generations of leaders," he said.
Ole Miss Chancellor Dan Jones noted past hurts and present imperfections.
"As we look back, we acknowledge the years of injustice endured by Mr. Meredith and countless others, express regret and offer our apology for the injustice," he said. "We also ... recommit ourselves to open doors of opportunity to everyone regardless of race or ethnicity ... and to continue our pilgrimage toward full reconciliation."
Douglass Sullivan-Gonzampáles remarked on the racial progress since Ole Miss' days of ignominy.
"In 2012, we have a president and an attorney general of the United States who herald a proud African heritage as a part of their identity," he said. "Who in 1962 could have imagined such a great moment as we celebrate here tonight? Well, James Meredith and a thousand others did so."
Holder urged Ole Miss students to "challenge our nation to aim higher, to become better and to carry forth the fundamental ideals on which this country was founded.
"This is your solemn obligation," he said. "It is also your breathtaking opportunity."