He told the Washington Post: "Because there was no response from the other passengers on the flight at the time, I thought, 'Okay, well, somebody needs to know what happened here.'".
A few rows behind him, a ruddy-faced man with gray hair and dark-rimmed glasses was yelling at a black woman seated along the aisle.
However, the absence of a public apology to the passenger subjected to the rant and allowing her aggressor to remain on board has people vowing to never fly with the airline again.
Mr Lawrence said it was a "horrible, frightful situation" and that he was "shocked" that Ryanair "allowed something like this just to go unchecked".
"I spoke to the pilot at the end of the flight", Lawrence said.
"He pushed past the woman and went to his seat", Lawrence said, adding that the rest of the video features the "most disgusting exchange of racial slurs and foul language".
A video posted online showed a white man shouting racist insults at an elderly black woman sitting in the same row and demanding she move.
Commenting on Facebook, one woman said: 'Glad to see the man behind them intervened. "You need a wash".
Indicating the seat between them, he can be heard saying: "I hope somebody sits there because I don't want to sit next to your ugly f****** face".
When one passenger tries to intervene and stop the argument, the unruly man says, "I will carry on as far as I can with this ugly black bastard".
Ryanair sparked outrage after apparently failing to remove the man, with Labour MP for East Hull Karl Turner saying the airline "failed spectacularly".
In the video, widely circulated on social media and recorded by passenger David Lawrence, the elderly man appears to be refusing to sit next to her and threatens to "push" her to another seat if she isn't moved.
The Twitter account @StanceGrounded posted the video on Sunday and had 28,000 retweets by 2pm.
The woman's daughter told HuffPost UK: "Mum's really feeling upset and very stressed about this situation, on top of the grief she's already experiencing".
"I'm upset about the whole thing too - the fact that the passenger wasn't taken off the plane and how the situation was dealt with".
Throughout the video, the man refers to both the woman's skin colour and accent in derogatory terms.
The daughter said she had taken her mother, who is a Windrush Generation migrant who came to the United Kingdom from Jamaica in the 1960s, on holiday to mark one year since the death of her father.
A spokesperson for Ryanair said: 'We have reported this to the police in Essex and as this is now a police matter, we can not comment further'.