The 36-year-old was in her home in Galashiels, in the Borders, when the attacker entered the property at 10pm on Friday.
She was sexually assaulted for a sustained period of time at her home in Beech Avenue, Langlee, police said.
The man is white, 5ft 7in and skinny, with dirty-blonde hair. He has a tattoo on the back of his neck, a burn mark on his right forearm and a cut on his right index finger, which was bleeding.
He was wearing blue jeans with a red belt, a blue top with vertical stripes and may have been under the influence of alcohol.
Police are urging the public to help them find the man.
"The victim has been subjected to a sustained and violent attack within her own home by an unknown male and a major police investigation has been launched to trace this individual," said Detective Inspector Derek Long from Lothians and Scottish Borders division of Police Scotland.
"We have an excellent description of the suspect and hope the Galashiels community can help us identify him and bring him to justice. He is known to have been in this area throughout Friday evening and into the early hours of Saturday morning."
Police say they will carry out high-visibility patrols in the Langlee area and issued a reminder for people to ensure their homes are secure at all times.
Anyone with information about the assault, or recognises the description of the attacker, can call police on 101 or Crimestoppers anonymously on 0800 555 111.