The court ruled in favor of the Westboro Baptist Church of Topeka, Kan. and said that protesters have the right to picket despite the pain they may cause families.
The 8-1 decision upholds an appeals court ruling that threw out a $5 million judgment to the father of a dead Marine who sued church members after they picketed at his son's funeral.
Matthew Snyder died in Iraq in 2006. During his funeral in Westminster, Md., members of the church protested to draw attention to their incendiary view that U.S. deaths in Afghanistan and Iraq are God's punishment for the nation's tolerance of homosexuality.
Chief Justice John Roberts said that the court is choosing "to protect even hurtful speech on public issues to ensure that we do not stifle public debate."
The Associated Press contributed to this report.