Du Toit was a colossus for the Springboks during the World Cup and dominated the breakdown during the final win over England, helping South Africa secure seven turnovers and proving a menace for the English throughout the match.
He also made 11 tackles and set up fellow player of the year nominee Cheslin Kolbe for the decisive final try in the 32-12 win.
"This is probably one of the best moments of my life," said du Toit.
"I think it is the two biggest experiences in the rugby world that you can get. It is as unbelievable experience for me and I couldn't be happier at the moment."
The Springboks were named team of the year.
Erasmus, who will be stepping down as South Africa coach to return to his role as the country's director of rugby, not only secured the Springboks' third World Cup title but also led them to a first Rugby Championship win since 2009.
Under Erasmus, South Africa have only lost once in 2019, in the pool stages to old rivals New Zealand.
When he took over in March 2018, South Africa were ranked seventh in the world but they have returned to their traditional forwards-based game with extraordinary results.
"This has been a long journey to keep believing and trusting and not getting frustrated with each other, keeping the belief going," said Erasmus.
"For me, it is significant that, no matter what, the boys always kept South Africa above their own interests, above their own egos and always kept the Springboks and South Africa's interests up there."
Unsurprisingly, given their success over the past 12 months, South Africa also collected the team of the year award.
Captain Siya Kolisi collected the award on behalf of his team.
"I think it is probably going to sink in when we get home and see how people are back at home," said Kolisi.
"They have really been driving us, they have been behind us. I think coach said it earlier they have been a huge part of our success as a team and we are looking forward to going back home and celebrating with them."
Former Ireland No.8 Jamie Heaslip, who won 95 caps for his country and retired last year, received the International Rugby Players' special merit award.
Try of the year went to New Zealand halfback TJ Perenara following a stunning score in the World Cup pool game against Namibia.
Ruby Tui was named women's sevens player of the year.