“Merry Christmas Baby” is an R&B Christmas standard credited to Lou Baxter and Johnny Moore and originally recorded in 1947 by Johnny Moore’s Three Blazers, featuring the singer and pianist Charles Brown. Charles Brown tells the story this way: “Leon René had Exclusive Records. They needed a song; Bing Crosby had “White Christmas”. Lou Baxter, who was a songwriter and used to hang around Johnny Moore and the Blazers, said ‘Charles, I want you to do one of my songs because I need money.’ He had to have an operation on his throat, he had throat cancer. If we did one of his numbers they would give him a $500 advance. So I looked in the satchel, I took the satchel (of songs) home that night and I looked in there, I looked at all them things, and it didn’t impress me. I saw “Merry Christmas Blues”, but the idea struck me. I said this would be a good idea, but it wasn’t like what he had written. I wrote the title “Merry Christmas Baby”, and I wrote the words, how I was going to sing it, and I mapped it out, played the piano, and I presented it to Johnny Moore. We didn’t know it was going to be a great big hit, but I thought it was unique. Leon Rene said put the celeste on it. I had never played one. He said it’s just like the piano, put it on the side of the piano. ‘Cause they didn’t have all these synthesizers. He said just play it (on the intro) like you play the piano then get back to the piano. Exclusive never paid copyrights. Hollywood Records took over, lawyers for creditors said artists would get their money, but it never happened. Don Pierce [Hollywood Records] never paid a nickel. Charles lost his letter. When Exclusive Records was sold, the artists/creditors got nothing. Leon Rene promised the artists the money would come. Never happened.”And Johnny Moore did the deal with Lou Baxter and put his own name on it as well, apparently. 
During the 1940s, when Hollywood celebrities attended parties, they were expected to perform. In 1944, Frank Loesser wrote “Baby, It’s Cold Outside” for his wife, Lynn Garland, and himself to sing at a housewarming party in New York City at the Navarro Hotel. They sang the song to indicate to guests that it was time to leave. Loesser often introduced himself as the “evil of two Loessers” because of the role he played in the song.
Garland wrote that after the first performance, “We become instant parlor room stars. We got invited to all the best parties for years on the basis of ‘Baby.’ It was our ticket to caviar and truffles. Parties were built around our being the closing act.” In 1948, after years of performing the song, Loesser sold it to MGM for the 1949 romantic comedy Neptune’s Daughter. Garland was furious. She wrote, “I felt as betrayed as if I’d caught him in bed with another woman.”
Accounts vary as to when and where Berlin wrote the song. One story is that he wrote it in 1940, in warm La Quinta, California, while staying at the La Quinta Hotel, a frequent Hollywood retreat also favored by writer-director-producer Frank Capra, although the Arizona Biltmore also claims the song was written there. He often stayed up all night writing—he told his secretary, “Grab your pen and take down this song. I just wrote the best song I’ve ever written—heck, I just wrote the best song that anybody’s ever written!”