Kevin Spacey, the two-time Academy Award-winning actor, appeared briefly on Wednesday in a London courtroom for the first day of a trial on multiple charges of sexual assault.

Mr. Spacey, 63, is facing 12 charges related to incidents that the prosecution says involved four men and occurred between 2001 and 2013. For much of that period, he was the artistic director of the Old Vic theater in London.

In two previous hearings over the past year, Mr. Spacey pleaded not guilty to all those charges.

On Wednesday morning, in a wood-paneled courtroom at Southwark Crown Court — a venue typically used for high-profile British criminal cases — Mr. Spacey sat in a large transparent box in the middle of the room, wearing a dark blue suit, light blue shirt and pink tie, while the jury was sworn in.

The judge overseeing the case, Mark Wall, told the jurors that Mr. Spacey would “be gratified that many of you know his name, or have seen his films,” but said that would not disqualify them from…