UNAIDS said it had named the Brazilian vice captain as its "International Goodwill Ambassador" in a bid to "mobilise football fans around the world, particularly young people," to join its efforts to stymie the spread of HIV and root out discrimination of people living with the virus that leads to AIDS.
UNAIDS chief Michel Sidibe said he was convinced Luiz would "make a big difference reaching out to millions of young people," pointing out that with the player's homeland hosting the World Cup in June, "everyone's eyes will be on Brazil and David will be an inspiration both on and off the pitch."
"In football, players come together to produce results. In the same way we must unite and as a team get to zero new HIV infections," he said.
Luiz, who also plays professionally for English Premier League club Chelsea, said he was honoured by his appointment, adding he wanted to "use this position to spread the word about how to overcome AIDS around the world."
Of the estimated 35.3 million people living with HIV around the world, some 5.4 million are 10 to 24 years old, and many of them do not know they are carrying the virus, according to UNAIDS.
Around 780,000 people aged between 15 and 24 contract the virus each year.