A forensic official in the country has told the Associated Press news agency that Rebecca Dykes, who worked at the embassy in the capital Beirut, was strangled with a rope.
The unnamed official added that authorities are investigating the exact cause of her death and whether she was sexually assaulted.
A security official, who also spoke on condition of anonymity, told AP Ms Dykes' body was discovered by the side of a road east of Beirut on Saturday.
According to Lebanese media reports, choke marks were found on Ms Dykes' neck and she had been raped.
A family spokesman said they were "devastated by the loss of our beloved Rebecca".
"We are doing all we can to understand what happened," he added.
According to Ms Dykes' LinkedIn profile, she had been working as a programme and policy manager for the Department for International Development (DfID) on the UK government's Conflict, Stability and Security Fund programme in Lebanon.
A DfID spokesman said: "Our thoughts are with Becky's family and friends at this very upsetting time.
"There is now a police investigation and the FCO (Foreign Office) is providing consular support to Becky's family and working with the local authorities."
The Foreign Office has said it is in contact with authorities in Lebanon.
"Following the death of a British woman in Beirut, we are providing support to the family," a spokesman said.
"We remain in close contact with local authorities. Our thoughts are with the family at this difficult time."
The Lebanese Ambassador to the UK, Hugo Shorter, tweeted his condolences.
He said: "The whole embassy is deeply shocked, saddened by this news. My thoughts are with Becky's family, friends and colleagues for their tragic loss. We're providing consular support to her family & working very closely with Lebanese authorities who are conducting police investigation."
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