Ahead of Tuesday night's affair, convention officials released a clip of the segment, in which Cindy McCain appears via audio. In the video, titled "An Unlikely Friendship," Cindy McCain said of the two, "They would just sit and joke. It was like a comedy show sometimes to watch the two of them."
The rest of the clip shared some personal details about their friendship over the years.
"It was a friendship that shouldn't have worked. John, a former Navy pilot just released from a North Vietnamese prison. Joe, a young senator from Delaware," the narrator says in the preview clip. "But in the 1970s, Joe was assigned a military aide for a trip overseas."
"I was a Navy Senate liaison and used to carry your bags on overseas trips," John McCain is heard saying in the video, which is pulled from a 2016 clip from the Senate floor.
"The son of a gun never carried my bags. He was supposed to carry my bags there but he never carried my bags," Biden replied back, in a clip from his 2017 speech at the Liberty Medal ceremony.
"John and Joe traveled thousands of miles together," the narrator says. "The families got to know each other, gathering for picnics in the Bidens' backyard."
Cindy McCain's appearance at the DNC comes after four Republican leaders, including former Ohio Gov. John Kasich, offered their support for Biden on the first night of the mostly-virtual convention. On Tuesday, she said she was "honored" to accept an invite from the Biden team to be part of the video.
"My husband and Vice President Biden enjoyed a 30+ year friendship dating back to before their years serving together in the Senate, so I was honored to accept the invitation from the Biden campaign to participate in a video celebrating their relationship," McCain tweeted.
At that time, she said the current Republican Party is "not the party of Abraham Lincoln... nor the party of Ronald Reagan."
"That was a tough torch to carry and, as John said, there were many lonely days because he always said what was on his mind," she told Karl. Cindy McCain added at the time that her husband "never did anything deliberately to be hurtful or anything… I don't see anybody carrying that mantle at all, I don't see anyone carrying the voice -- the voice of reason."
President Donald Trump has been notably critical of John McCain over the years, frequently insulting his military service and capture as a prisoner of war in Vietnam.
"He's not a war hero. He's a war hero because he was captured. I like people who weren't captured," Trump said while on the campaign trail in 2015.
As president, he has railed against the late Arizona senator's vote against repealing Obamacare, saying he was "never a fan" and "never will be." He continued to criticize John McCain months after his death from brain cancer in 2018.
For his part, McCain mostly refrained from the type of personal attacks that Trump levied against him, though he did critique the president's tone and use of executive power.
"I hope we can again rely on humility, on our need to cooperate, on our dependence on each other to learn how to trust each other again and by so doing better serve the people who elected us," he said the day after his landmark health care vote. "Stop listening to the bombastic loudmouths on the radio and television and the Internet. To hell with them. They don't want anything done for the public good. Our incapacity is their livelihood."
ABC News' Alisa Wiersema contributed to this report.