Kevin Spacey, the two-time Oscar-winning actor known for his movie and TV roles including “House of Cards,” was on Wednesday found not guilty by a jury in Britain of nine counts of sexual assault.

Almost six years after allegations of inappropriate behavior began to emerge against Mr. Spacey on both sides of the Atlantic, a jury at Southwark Crown Court in London took just over 12 hours to reach its decision.

As the verdicts were announced, Mr. Spacey, 64, stood in a transparent box in the middle of the courtroom, wearing a dark blue suit and looking unemotional as he faced the jury.

But when the final “not guilty” was read out, the actor, whose birthday falls on Wednesday, began to cry and sighed heavily with relief.

During the almost monthlong trial in London, the court heard from four men who said that Mr. Spacey assaulted them between 2001 and 2013. For most of that time, the actor was the artistic director of the Old Vic theater, a major London playhouse.

One complainant…