Born in Hartford, Connecticut, Thompson was educated at the Loomis School, and graduated from there in 1947. He attended Yale University, where he joined the Elizabethan Club and the literary magazine, and graduated with a B.A. in 1951. He also attended Columbia University for three summers. After Yale, he studied for a year in Rome on a Fulbright Scholarship from 1951 and 1952.

Selden is best known as the author of several books about the character Chester Cricket and his friends. The first book, The Cricket in Times Square, was a Newbery Honor Book in 1961. Selden explained the inspiration for that book as follows:

"One night I was coming home on the subway, and I did hear a cricket chirp in the Time Square subway station. The story formed in my mind within minutes. An author is very thankful for minutes like those, although they happen all too infrequently."

In 1974, under the pseudonym of Terry Andrews, Selden wrote the novel The Story of Harold, the story of a bisexual children's book author's various affairs, friendships, and mentoring of a lonely child. The book is very descriptive of the seventies, including the sexual revolution. Graphic scenes of sado-masochism, orgies and other sexual acts, are narrated by Harold, the main character. It could be construed as somewhat autobiographical in the sense the author writes of a character who writes children's books. The relationship to the boy and also the author's own feelings regarding his own existence are the main keys in this novel.

Selden remained unmarried; a resident of Greenwich Village in New York City, he died there at age 60 from a gastrointestinal hemorrhage.

He wrote several sequels and other books in a series, which totaled seven books in all:

• The Cricket in Times Square
• Tucker's Countryside
• Harry Cat's Pet Puppy
• Chester Cricket's Pigeon Ride
• Chester Cricket's New Home
• Harry Kitten and Tucker Mouse
• The Old Meadow

His other books include:

• The Genie of Sutton Place
• Oscar Lobster's Fair Exchange
• Sparrow Socks (1965)