The scene-stealer at Thursday's Democratic convention was not a politician or Hollywood A-lister, but a 13-year-old boy whose stutter has substantially improved through the help of the man at the center of the gathering itself: Joe Biden.

Brayden Harrington said in a touching video aired on the event's final night that he had met Biden while the candidate with blue-collar roots campaigned in New Hampshire earlier this year.

"Without Joe Biden, I wouldn't be talking to you today," the young boy wearing braces and a wide smile explained.

"He told me that we were members of the same club. We stutter. It was really amazing to hear that someone like me became vice president," Brayden said, halting on some of the words.

As a child, Biden, now 77, was hampered by a stutter so severe he was cruelly nicknamed "Dash."

The candidate occasionally tells the story on the campaign trail of his effort to overcome the condition, about how he read from books by Irish poets and practiced his diction at night with a flashlight in front of a mirror.

Brayden said Biden sat him down and told him about the poems that he read aloud and practiced, and showed the boy how he marks his speeches in a way that helps make them easier to recite.

"I'm just a regular kid and in the short amount of time, Joe Biden made me more confident about something that's bothered me my whole life," the boy said. "Joe Biden cared. Imagine what he can do for all of us."

Braydon was praised online for his courage, and he was trending on Twitter shortly after his appearance.

Former Democratic congresswoman Gabrielle Giffords, who was shot in the head in 2011 and now has a speech impediment, tweeted: "Speaking is hard for me too, Brayden. But as you know, practice and purpose help. Thank you for your courage and for the great speech!"

Outspoken singer Bette Midler wrote: "Wow! What a story! #BraydenHarrington! BRAVO!"

And praise for Braydon crossed political lines, as even Kellyanne Conway, an aide to President Donald Trump, tweeted: "Way to go, Brayden!"

'They can call me'

A video about Biden's life that ran before he accepted his party's nomination Thursday night mentioned the candidate's childhood stutter, and about how his mother drove him back to school when he came home saying he had been mimicked by a teacher.

"Did you say to my son Mr. B-B-Biden?" Biden says in the clip, quoting his mother.

"The nun said 'I was just trying to make a point.' My mother stood up (and said) 'If you ever talk to my son like that again I'll come back and rip that damn bonnet off your head, do you understand me?"

The issue became visible during the campaign when he stumbled multiple times during the Democratic debates.

In a revealing interview last year in US magazine The Atlantic, Biden acknowledged he still gets caught on words as an adult, which could help explain some of his slips.

The candidate told a town hall in February that when he meets someone with a stutter, he often gives them his private number.

"They can call me," he said.