Kagan, who was confirmed and sworn in during the summer, is the third woman sitting on the current panel and the fourth female justice ever. U.S. President Barack Obama nominated her to succeed John Paul Stevens.
Kagan sat in the same chair used for investiture ceremony of every Supreme Court justice since Lewis F. Powell Jr. in 1972, the court's Public Information Office said.
Obama attended the ceremony seated next to retired justices Stevens, Sandra Day O'Connor and David Souter.
Chief Justice John Roberts recognized Obama, saying, "You are always welcomed here."
After the clerk read her commission, Roberts administered judicial oath to Kagan.
Kagan, the 100th associate justice of the Supreme Court, took her seat on the bench -- the last seat on the right.
Kagan and Roberts were photographed outside of the Supreme Court building, chatting in the sunshine, after the ceremony.
The Supreme Court's term beings Monday.