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Just as the title says: Would a chess game go on indefinitely if both players played the absolute best move each turn? (assuming there is no draw) Or is it white that's going to win?

Is it even possible to be sure about that? Since even engines like Stockfish don't have a 100% accuracy rate.

It's not really a "does white have the advantage" question, rather "if we make the best move each turn, will it ever end?"

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It doesn't matter whether the players play good moves or bad moves there is a maximum possible number of moves. There is a rule which guarantees this - the 75 move rule. It says that if 75 moves are played without either a pawn move or a capture then the game is drawn.

The relevant article of the FIDE Laws of chess is 9.6.2-

9.6 If one or both of the following occur(s) then the game is drawn:

9.6.1 the same position has appeared, as in 9.2.2 at least five times.

9.6.2 any series of at least 75 moves have been made by each player without the movement of any pawn and without any capture. If the last move resulted in checkmate, that shall take precedence.

So, once every 75 moves a piece must be captured or a pawn moved (forward). Eventually all the pawns have queened or been captured and all the pieces captured and only the kings are left - which is a draw.

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    Perfectly correct, but I feel that this is only a partial answer. IMO it should be added a note (or link) saying that nobody knows whether white is going to win and nobody knows what the best move in any position would be.
    – user1583209
    Nov 27, 2018 at 22:34
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    For additional discussion of the theoretical maximum number of moves, see Longest chess game possible (maximum moves).
    – itub
    Nov 27, 2018 at 23:36
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    I would regard the FIDE laws as rules for the events that are subject to the organization's jurisdiction, rather than fundamental rules of the game itself. If e.g. the 75-move rule were replaced by a hypothetical rule that would proclaim Black victorious if the game went more than 500 moves and black had sufficient mating material, but stalemate and lack of mating material were still draws, would that change give Black a winning advantage, or could White--at worst--force Black into a choice between a stalemate and a loss?
    – supercat
    Nov 28, 2018 at 22:18
  • @user1583209 your statement that we don't know what PerfectPlay looks like is true ... but not actually relevant. It doesn't matter that we don't know what Perfect Play is ... because as outlined above, the game must be finite whatever Perfect Play looks like.
    – Brondahl
    Jan 20 at 8:26
  • @Brondahl If by "finite" you mean that the game ends because of the 75 moves rule that is debatable, depending on whether you consider FIDE laws as part of the game (see comment by supercat). Also note that the OP specifically excludes draws.
    – user1583209
    Jan 31 at 1:22

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