"This is a wonderful crowd," Carter mused. "It's even bigger -- and I hate to say this -- than it was last year."
Several in the crowd of graduates and parents chuckled and clapped.
"I don't know if President Trump will admit that or not," he said, a joking reference to the Trump administration's assertion that the crowd for his 2017 inauguration was the largest ever.
The university estimated that 8,000 graduates participated in the rain-soaked ceremonies on the school's campus in Lynchburg, Virginia.
The former president said that one of the greatest human rights problems is "discrimination against women and girls in the world."
Carter said he hoped Christians and all religions would "come together to promote the word of the gospel" as nuclear threats and divisions continue to be sown by politicians and the public.
Carter was the third commencement speaker at Liberty University to have held the office of president, the university said on its website: Trump (in 2017) and George H.W. Buah (in 1990) spoke at the school's graduation while still in office.