At dusk, honor guard pallbearers carried the flag-draped casket to his grave site, between two maple trees where a 2 1/2-foot white cross stood and a simple marble foot stone read: "Edward Moore Kennedy 1932-2009."
"There's a certain fitness at having a burial at the dying of the day because we know that the sun will come back again tomorrow, and as we think of Teddy, we know that his new life begins," Cardinal Theodore McCarrick, archbishop emeritus of Washington, told mourners.
"They called him the lion of the Senate and, indeed, that's what he was. His roar and his zeal for what he believed made a difference in his nation's life," added McCarrick, a longtime friend of Kennedy, a lifelong Catholic. "We were always touched by his passion for the underdog."
McCarrick read parts of a letter Kennedy had given to U.S. President Barack Obama to hand deliver to Pope Benedict XVI in which the senator asked for the pontiff's prayers and said he tried to champion the rights of the poor, welcome immigrants, fight discrimination, end the death penalty and ensure healthcare for all.
Family members and others at the private service, including Vice President Joe Biden, prayed, and some wept by the grave site, decorated with white hydrangeas and white roses, as taps played.
Earlier, Kennedy's body arrived in Washington, greeted by thousands of mourners who applauded and sang "America The Beautiful."
The motorcade arrived at the U.S. Capitol, where members of Congress and staffers thronged the steps in the late afternoon on a muggy day in Washington.
Outside the Capitol, Kennedy family members shook hands, hugged and waved to those who showed up to say goodbye, many of them holding American flags, some of them crying.
Rep. Patrick Kennedy, D-R.I., one of Kennedy's sons, said he and his brothers and sisters were proud of their father.
"He was only great because he had great people supporting him," the son said. "This country has out-poured its soul and heart these last few days to say what a difference his life has made to this country."
The plane carrying Kennedy's body arrived at Andrews Air Force Base in Maryland about 4:30 p.m. EDT before the casket made its final trip to Washington.
As family members headed to the cemetery from Washington, they opened the windows of their limousine and waved to the many people lining the streets.
Kennedy's body had been escorted Saturday after a mass at the Basilica of Our Lady of Perpetual Help in the Mission Hill neighborhood of Roxbury, Boston's largest black district.
Kennedy died Tuesday of brain cancer at 77. He outlived his brothers by more than 40 years and became the only Kennedy brother of his generation to die of natural causes.
Obama, delivering one of the eulogies at the funeral mass, remembered Kennedy as a "champion of those who had none; the soul of the Democratic Party; and the lion of the U.S. Senate."