The 34-year-old, Brazil's all-time leading scorer, comes back following a prolonged absence due to a series of injuries that kept him out for much of the qualifying campaign, as the five-time champions pursue a record-extending sixth title.
As dozens of journalists gathered at Rio de Janeiro's Museum of Tomorrow for a ceremony featuring music acts and celebrity guests, all eyes were on Ancelotti's decision on whether to include Neymar in the squad.
The 66-year-old Italian, who took over Brazil last year, had not previously called the former Barcelona and Paris St Germain player. He told Reuters earlier this month that Neymar's inclusion would be based on fitness and form, not sentiment.
"I had all the information I needed to make the best possible decision and create a list with as few errors as possible," Ancelotti said at Monday's ceremony.
Neymar, who has 79 international goals but has not featured for Brazil since 2023, has faced questions about his fitness and form following an injury-marred spell at Al Hilal and an underwhelming return to his boyhood club Santos last year.
The forward said on Sunday he was satisfied he had done all he could to prove he was fully fit and deserved a place in the squad. "Physically, I feel great. I've been improving with every game," he told reporters after Santos' 3-0 defeat by Coritiba.
His inclusion left less space for other forwards, with Chelsea striker Joao Pedro and Real Betis star Antony both being left out of the squad.
Brazil's 2026 World Cup squad
Goalkeepers: Alisson (Liverpool), Ederson (Fenerbahce), Weverton (Gremio)
Defenders: Alex Sandro (Flamengo), Danilo (Flamengo), Leo Pereira (Flamengo), Bremer (Juventus), Douglas Santos (Zenit St Petersburg), Gabriel Magalhaes (Arsenal), Ibanez (Al-Ahli), Marquinhos (Paris Saint-Germain), Wesley (Roma)
Midfielders Bruno Guimaraes (Newcastle), Casemiro (Manchester United), Danilo (Botafogo), Fabinho (Al-Ittihad), Lucas Paqueta (Flamengo).
Forwards: Endrick (Lyon), Gabriel Martinelli (Arsenal), Igor Thiago (Brentford), Luiz Henrique (Zenit), Matheus Cunha (Manchester United), Neymar (Santos), Raphinha (Barcelona), Rayan (Bournemouth), Vinicius Junior (Real Madrid)