McManus was born and raised in Sandpoint, Idaho. His father, who served in the 42nd Division under Douglas MacArthur during World War II, died when he was six. Although his mother later remarried, for the most part he was raised by his mother, grandmother, and older sister Patricia (referred to in his childhood stories as "the Troll"). After high school, McManus worked construction and other such jobs until he had saved enough money to attend Washington State College, now Washington State University. He is married to Darlene "Bun" McManus and has four daughters.

McManus writes mostly about his outdoor adventures from his childhood with semi-fictional characters such as his old woodsman mentor Rancid Crabtree and his childhood friends. The stories' humor is mostly based on elaborate exaggerations of his surreal adventures into the outdoors. McManus's writing is characterized by a dry wit that has drawn comparisons to Mark Twain and Robert Benchley.

As of 2007, his most recent work is Avalanche, the second in a series of mystery novels starring the character Sheriff Bo Tully. Other departures from his column-collections include Kid Camping From Aaaaii! To Zip (1979, an alphabetized, and partially serious, listing of useful tips and concepts for beginning campers); Whatchagot Stew (1989, both a cookbook and a less-fictionalized memoir of his childhood); and The Deer On A Bicycle (2000, a discussion of the art of humor writing.)

Some of his stories have been adapted as stage-plays.

Magazine Columns Collections

• A Fine and Pleasant Misery (1978)
• They Shoot Canoes, Don't They? (1981)
• Never Sniff A Gift Fish (1983)
• The Grasshopper Trap (1985)
• Rubber Legs and White Tail-Hairs (1987)
• The Night the Bear Ate Goombaw (1989)
• Real Ponies Don't Go Oink (1991)
• The Good Samaritan Strikes Again (1992)
• How I Got this Way (1994)
• Never Cry "Arp!" And Other Great Adventures (1996)
• Into The Twilight, Endlessly Grousing (1997)
• Kerplunk!: Stories (2007)

Sheriff Bo Tully Mysteries

• The Blight Way: A Sheriff Bo Tully Mystery (2006)
• Avalanche: A Sheriff Bo Tully Mystery (2007)
• The Double Jack Murders: A Sheriff Bo Tully Mystery (2009)

Other

• Kid Camping from Aaaaii! To Zip (1979)
• Whatchagot Stew (1989), co-written with Patricia McManus Gass
• The Deer on A Bicycle (2000)
• The Bear in the Attic (2002)

McManus' shorter works include a recurring cast of fictitious characters and running jokes, both from the stories set in his childhood and as an adult. The foremost among the childhood stories is his "mentor" Rancid Crabtree, a colorful woodsman who lives near Pat's childhood home. Other recurring characters are his childhood best friend, Crazy Eddie Muldoon, and his adulthood friends, the goofy Retch Sweeney and his straitlaced neighbor, Al Finley. Throughout the majority of the stories is a recurring theme of McManus's lifelong love of hunting and fishing--which is mostly an excuse to just enjoy the outdoors, often in good company. Most of his friends likewise enjoy hunting and fishing, even if they aren't particularly good at it. McManus, in his stories, has a certain amount of disgruntlement for people who take great pleasure in the minutiae of various sports (such as encyclopediac knowledge of firearms calibers and ballistics). He refers to firearms enthusiastics as 'gun nuts' and treats their excited sharing of the fine points of ballistic arcs and grain sizes as something to be endured to get on a good hunting trip.

Some of the elements show up in his longer works, and are even worked into the plots. Bo Tully, the protagonist of the Bo Tully Mysteries, shares McManus' views about firearms--in the course of his job as Sheriff and his hobbies, Tully uses guns, knows about guns, but isn't particularly excited by them or even sentimental towards them. He is, however, aware that many people are. *** SPOILER FOLLOWS *** This even serves as plot point in one of the Bo Tully mysteries, Tully is investigating an absent murder suspect and sees that the man has a gorgeously mounted collection of antique, original, or unusual firearms--with a gap in it that would correspond to the type of handgun used in a murder. Tully realized it's likely that an ardent gun collector would be reluctant to destroy or permanently discard such a gun, and operates on the hunch that the murder weapon is hidden nearby and carefully preserved to prevent possible damage.