According to Journal 3, during his investigation on the secret scandals of the Northwest family in the manor, Ford encounters the young Preston Northwest and his pet fox "Hunter", but when he mentions the Great Flood of 1863, Preston forcefully escorts Ford out of his manor.
In "Irrational Treasure," they celebrate Pioneer Day with Pacifica, their daughter. They pose together for a family photo after the opening ceremony, and later they both laugh at an insult Pacifica makes to Mabel before going home.
In "The Golf War," he and Priscilla are seen at Ye Royal Discount Putt Hutt with Pacifica, and they stand by as she insults the Pines family. They later bring Pacifica back to the mini golf course for her competition against Mabel, pressuring her to win. They do not stay to watch because they have a party to attend.
In the "Society of the Blind Eye" it is revealed that he has had his memories erased. His memories may have been heavily linked to the goings-on of the Blind Eye Society, since it was on the shelf in The Hall of the Forgotten, next to McGucket's memories. It is possible that Preston's tube is also on a pressure sensitive plate.
In "Northwest Mansion Mystery," he and Priscilla are preparing for their massive annual party, open only to the rich and the super-rich. He is shown to ring a bell to silence Pacifica into obedience whenever she speaks out. He was also aware of the curse placed upon the family by the Ghost of Northwest Manor, but refused to allow the common folk in, fearing that his family's reputation would be ruined. Instead, he has Pacifica recruit Dipper to deal with the ghost, making her keep the real reason for the haunting a secret. After Dipper captures the ghost, he is told of the reasons for his cursing the Northwest family, and Dipper angrily confronts the Northwest family. Preston coldly rejects Dipper's tirade and prevents Pacifica from telling Dipper that he forced her to lie. When the ghost escapes and starts turning the guests to wood, Preston has his family and butler hide in a panic room, leaving their guests to their fate rather than break the curse by letting in the common folk. However, Pacifica stands up to her father, opening the gates and breaking the curse, leaving Preston dismayed at all the "riff-raff" entering the party.
In "Weirdmageddon Part 1," Preston attempts to offer his allegiance to Bill after he melts the Nathaniel Northwest Statue, despite Pacifica scorning him for it. Bill instead chooses to shuffle his facial orifices, disfiguring and mutating Preston's face. Preston screams and then collapses in front of a horrified Pacifica and Priscilla as Bill laughs sadistically.
By "Weirdmageddon 3: Take Back The Falls," Preston and Priscilla have been petrified by Bill and their bodies have been used to build Bill's throne. They return to normal (and Preston's face has been reconfigured) when Dipper collapses the throne. Pacifica calls out to her parents and Sheriff Blubs shoves Preston and his wife out of the way in order to reach the resuscitated Deputy Durland. Later, after Pacifica initially refuses to hold Old Man McGucket's hand and form the circle needed to defeat Bill, Preston, doing the right thing for once, advises her to "touch the hillbilly," adding that no one in their family has ever done so before. After Bill is defeated, Preston is shown weeping outside the gates of his mansion, which he was forced to sell in order to retain his fortune, which he had squandered by allying with Bill and investing in Weirdness bonds. Ironically, McGucket buys the mansion and becomes its new owner.
Mr. Northwest enjoys being wealthy and takes pride in being a descendant of Nathaniel Northwest, the alleged founder of Gravity Falls, Oregon. It appears that he and Priscilla Northwest are as snobbish as their daughter, and support her being rude to others. However, Preston proves to be significantly worse than he initially seems.
He is revealed to be a truly unmerciful, ruthless, and callous man who sees anyone of the lower class as simply tools to be manipulated (unlike his daughter who is simply a jerk). He also doesn't seem to care for the fellow rich that much either, being willing to leave others to their deaths if it means preserving the Northwest family name, as shown when he tries to persuade Pacifica from opening the gates to their party rather than breaking the curse. He is extremely controlling, authoritative, traitorous, cunning, argumentative and emotionally abusive to Pacifica, using a bell to keep his daughter in check to his standards. It is implied that he doesn't truly care for Pacifica either, and simply sees her as a tool to maintain the Northwest name. 
Preston Northwest has short dark brown hair and a dark brown mustache. He has prominent cheekbones, and a large, rectangular nose. For Pioneer Day, he dressed up in a top hat and a suit similar to Priscilla's dress. He wears a gold ring on his middle finger on his left hand. He generally wears a black suit with a white undershirt and a green tie.
- 203. "The Golf War"
- 207. "Society of the Blind Eye" (mentioned)
- 210. "Northwest Mansion Mystery"
- 215. "The Last Mabelcorn" (pictured)
- 217. "Dipper and Mabel vs. the Future" (no lines)
- 218. "Weirdmageddon Part 1"
- 220. "Weirdmageddon 3: Take Back The Falls"
"Good one, daughter!"
"Oh, and whatever happens, just remember one thing: you're a Northwest. Don't lose."
"Look at who you're talking to, boy. I'm hosting a party for the most powerful people in the world. Do you think they'd come here if they had to rub elbows with your kind?"
"Pacifica Elise Northwest, stop this instant! We can't let the town see us like this! We have a reputation to uphold! Now come into the panic room, there's enough mini-sandwiches and oxygen to last you, me, and a butler for a full week. (whispering) We'll eat the butler!"
"I would just like to say that as a rich capitalist I welcome your tyrannical rule. Perhaps I could be one of your, uh... horsemen of the apocalypse?"
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