1973 was a year in the 20th century.
- Timeline 1
- Timeline 2
- Dates Unknown:
- After an elderly Biff Tannen made himself rich by traveling back to 1955 to give his younger self a Grays Sports Almanac, his younger self became a millionaire by gambling as he knew the results before they happened. Using his wealth, Biff created BiffCo, and bought much of the property in Hill Valley, including Otis Peabody's Lone Pine Ranch.
- George McFly, Goldie Wilson, Stanford S. Strickland, Mrs. Blumberg (the editor of the Hill Valley Telegraph), Mark Dixon, Terry, and two other individuals turned the Hill Valley Civic Committee into a secret committee with the sole purpose of stopping Biff.
- The Hill Valley Telegraph was sold to The Washington Post, to prevent Biff from buying it. They published an article that was critical of BiffCo.
- Biff bought the Hill Valley Police Department, a television and radio station, and most of the property in Hill Valley.
- Thursday, March 15: George was to receive a book award from the Hill Valley Civic Committee. However, he never made it to the ceremony, as he was murdered by Biff Tannen in an alleyway.
- Dates unknown:
- Biff Tannen married Lorraine Baines McFly, who agreed to marry him in order to help her family, who had fallen on hard times due to the policies of BiffCo.
- Biff had Seargent Stan Reynolds of the Hill Valley Police Department, who owed Biff money, plant George McFly's wallet on Red the Bum.
- The Hill Valley Telegraph posted a story about Red being arrested for George's murder on the front page, with an article about Biff's wedding to Lorraine inside the paper. This infuriated Biff, as he felt the wedding should be on the front. He immediately placed a call to prepare his jet, so he could purchase The Washington Post and rename it The Biffington Post.
- Biff fired Bob Woodward and Carl Bernstein after they asked for permission to continue working on the story about the break-in at the Watergate Hotel.
- Three days later, Richard Nixon personally offered his thanks for stopping the articles about Watergate, and told Biff that he owed him. Biff asked for help running the paper, and Nixon told him that he'd send his own men there to work on the paper to keep Biff's hands clean (although Biff thought he was talking about the ink on the paper).
- Biff learned about the 22nd amendment to the United States Constitution that forbade a president for holding office for more than two four year terms.
- Biff began to bet on sporting events in order to gain money to bribe state legislators to repeal the 22nd amendment, which would allow Nixon to run for a third term in 1976.
- Loretta was born to Lewis and Louise.
- Dates Unknown:
Behind the scenes
- Friday, June 15: Neil Patrick Harris (Doogie Howser in The Earth Day Special) is born in Albuquerque, New Mexico.
- Back to the Future Part II (Mentioned only)
- Back to the Future: The Card Game (Mentioned only)
- Back to the Future: Biff to the Future