Mackenzie Phillips was born in Virginia, in the place called Alexandria and she is a daughter to John Phillips who was a singer for The Mamas & The Papas. Her mother was the first wife of John called Susan Adams. She is the sister to Jeffrey Phillips and the half sister for Tamerlane, Bijou and Chynna. She went to Highland Hall Waldorf School in California. She started to perform at the age of 12 where she was performing with the band and three of the classmates. One casting agent spotted them during a performance and they were given a chance to audition for the role in the American Graffiti and they got it.

Mackenzie Phillips got married two times. The first one was to the rock group manager called Jeffrey Sessler, a son of Freddie Sessler and their marriage lasted only 3 years and she got married to Michael Barakan who is a rock guitarist and he was known like Shane Fontayne professionally, they were married for 4 years. She has given birth to a son called Shane Barakan and he is a musician.

Mackenzie Phillips is known to have the lifetime trouble because of the drug abuse. She got arrested by the Los Angeles Airport Police when she was charged to have heroin and cocaine and it was found out while passing through the security screening. She pleaded guilty and she was sent to drug rehabilitation program. The case was dismissed when she completed the program. She was on the third season for Celebrity Rehab that took place in 2010. Afterwards, she discussed the recovery in The View episode of 2010. In 2009, Mackenzie Phillips released a memoir under the name of High on Arrival and she appeared in The Oprah Winfrey Show for an interview that lasted over an hour.  She said that she started to use the cocaine when she was only 11 and her father took the drugs with her and also injected her with the drugs. When she was 19 years old, she got high and got involved sexually with her father and it lasted over 10 years. She stopped the relationship when she was pregnant and she feared that her father may be the father of her baby.

Mackenzie Phillips got the stardom when she played a boy-crazy teenager called Julie Cooper and it was the character that got married and got the new name Horvath. She was being paid 50,000 dollars a week. However, this did not last because she failed to finish because of abusing drugs and alcohol. She decided to undergo treatment after two overdoses that were about to kill her.   Mackenzie Phillips got Honorary Best Actress Award in 2011.