Beckham is set to start the last-16 tie in a defensive midfield role after making his debut as a substitute in the 2-0 Ligue 1 home win over the same opponents on Sunday.
Beckham came on in the 76th minute and played a part in the second goal and has impressed Ancelotti enough in training for the coach to say he is ready to start at the Parc des Princes on Wednesday.
Ancelotti has earmarked Beckham to replace the suspended Marco Verratti to play alongside Blaise Matuidi or Clement Chantome in central midfield.
Ancelotti told a press conference: "He will play defensive midfielder. He has the experience and skills to help us.
"It's an important position on the pitch, he has to help the team in building the game. As we already know, he also has quality for taking set-pieces.
"In the interplay, he can play alongside Lucas and to the right of (Ezequiel) Lavezzi, or (Jeremy) Menez."
When asked about Beckham's fitness, Ancelotti said: "He is capable of playing a whole match."
The former Manchester United and England midfielder - who opted for Paris ahead of numerous other offers after the end of his contract with Los Angeles Galaxy in America's Major League Soccer - could once again face countryman Joey Barton who played for Marseille on Sunday.
The 37-year-old, who created headlines around the world when he chose to play for PSG and also with the decision to donate his five month salary to charity, has more than impressed his new coach.
Ancelotti added: "I understand that there has been an infatuation with him, but above all I like the Beckham who is at the centre of training. He works, he is humble every day."
Ancelotti also revealed he had decided to play Nicolas Douchez in goal against Marseille rather than first choice Salvatore Sirigu.
He said: "Nicolas Douchez plays tomorrow [Wednesday]. We have two great keepers and competition for this position is difficult.
"Salvatore Sirigu is the number one and (the) number two (is) Douchez. It is a choice, but he has the qualities to play."