The Oxford English Dictionary (OED – 3^rd edition, 2018) defines the American-English phrase yellow brick road as denoting a course of action or series of events viewed as a path to a particular (especially positive or desired) outcome or goal.

This phrase alludes to the road paved with yellow brick that leads to the Emerald City, as first described in the children’s fantasy novel The Wonderful Wizard of Oz (George M. Hill Company – Chicago, 1900), by the U.S author Lyman Frank Baum (1856-1919) and the U.S. illustrator and cartoonist William Wallace Denslow (1856-1915). In the novel, this road is mostly referred to as the road of yellow brick.

According to the OED, yellow brick road was first used in, and widely popularised by, the 1939 film adapted from the novel, The Wizard of Oz, produced by Metro-Goldwyn-Mayer, starring the U.S. singer and actress Judy Garland (Frances Gumm – 1922-69)—cf. also meaning and origin of the phrase ‘not in Kansas anymore’.

However, while it is true that yellow brick road does not appear in the novel and was popularised by the 1939 film, the expression occurred earlier, on two occasions, with allusion to The Wonderful Wizard of Oz:

1: The U.S. columnist and author Ringgold Wilmer ‘Ring’ Lardner (1885-1933) wrote the following in his column In the Wake of the News, published in The Chicago Daily Tribune (Chicago, Illinois) of Friday 22^nd December 1916:

The Wizard of Oz.
[Dict. JAL-RWL.]

Dorothy lived way in Kansas with her Uncle Hendry [sic] and her Aunt Em and everything was gray. Uncle Hendry said go down in the cellar. Dorothy hunted for Toto under the bed and one of his ears sticked [sic] up. The house blew away and Dorothy and Toto blew away.
When she woke up the gas [sic] was green and many little people were around. They call them Munchkins. The Which [sic] of the North came up. She was a good which [sic]. All the people said Dorothy killed the Which [sic] of the East. She was the wicked which [sic]. She didn’t kill her; the house blew on her.
So they told her to go to the Emerald City and see the Wizard of Oz. Get him to send her back to Kansas. You find it on the yellow brick road. Follow it.

2: Ruth Thiel, an eleven-year-old girl from Odessa, Washington, used the phrase in Marjorie Visits Oz, published in the Junior Spokesman-Review section of The Spokesman-Review (Spokane, Washington) of Sunday 19^th March 1922:

Marjorie lived with her father and mother in New York. She was the only child and was very spoiled. One day while she was playing in her nursery the wind suddenly blew her window open and snatched her up. Before she could get her breath she was set [sic] down just across the border of the “Deadly Desert.” She said, “Well, I suppose I am in the land of Oz.”
She then started out walking toward a yellow brick road she saw in the distance.

Immediately after the film was released, commercial advertisements made use of its characters, themes and expressions—among which yellow brick road. An interesting example is There’s Magic in the Air!, an advertisement for The Hecht Co., published in The Evening Star (Washington, D.C.) of Wednesday 27^th September 1939. Entirely based on The Wizard of Oz, this advertisement contains, in particular, transferred uses of yellow brick road:

● And that Yellow-Brick-Road they sing about! Follow it down to F St. at Seventh, and see if it doesn’t lead right into The Hecht Co. . . . and it’s paved with values and with Savings . . . for the young-in-heart of all ages.
[…]
● So follow the Yellow-Brick-Road—the Value-Road—down to F Street at Seventh . . . and bring all Washington with you . . . for the courtesy days of Hecht Month . . . because you’ll buy all your needs for Fall and Winter at
OUR GREATEST STOREWIDE SAVINGS OF THE SEASON!

The phrase denotes the means of access to the film in this advertisement for The Wizard of Oz, published in The Interior Journal (Stanford, Kentucky) of Friday 15^th December 1939:

Do you want thrilling adventure, merry music and laughter? Follow the yellow brick road to Metro-Goldwyn-Mayer’s biggest and most exciting picture.

The earliest figurative use of yellow brick road that I have found is from a letter by one Harold Jos. Jacobs, Jr., from Mathews, Louisiana, published in Aunt Jane’s Letter Club, in the Young People’s Paper section of The Times-Picayune (New Orleans, Louisiana) of Sunday 24^th September 1939:

LONG CAREER ENDS

Dear Aunt Jane and Cousins—Here I come to bid farewell to the Letter Club and all its works, much against my will. But one must. Place must be made for others and we graduates must hie ourselves to strange pastures to plow our way through the unknown and build the road, maybe a lovely “yellow brick road,” to future land.

The following image and caption are from a cartoon strip advertising The Wizard of Oz, published on Sunday 20^th August 1939 in several newspapers—for example in the San Francisco Examiner (San Francisco, California):

“We’re off to see the Wizard . . . the Wonderful Wizard of Oz!”

Dance down the Yellow Brick Road with Dorothy and the Scarecrow; thru orchards of apple trees which pick their fruit and throw it, too!