The phrase means that’s all there is, it’s finished, it’s over, the end. It originated in America, but the source is unknown.
The popular explanation is that it’s the punch line of a tale about an American GI serving overseas in the second World War. The GI is supposed to have received a letter from his sweetheart. He reads it to his colleagues: “Dear John.” They tell him to go on. “That’s it; that’s all she wrote.” However, there’s no evidence to support this explanation.
An example in print that precedes WWII is from a column in the Texas newspaper The Brownsville Herald, June 1935: “No power except that of the legislature can change the rolls. The assessor-collectors do not have the power, the commissioners’ courts do not have the power. That’s all she wrote and it’s final, the attorney general says in language much more eloquent and technical.”
Ernest Tubb wrote a country music song called That’s All She Wrote and published it in 1942. It seems likely that Tubb took the expression from popular usage. It’s possible, of course, that the expression was in use prior to 1935. Such expressions are often in use long before they appear in print.
American researcher Garson O’Toole, writing on the American Dialect Society mailing list, found three examples of “that’s all she wrote” from 1942, but all of them were in civilian contexts, so the prevailing view that the idiom is from World War Two servicemen being dumped by Dear John letters is no longer sustainable.
..…….
And that’s all I wrote, folks. I’ve been publishing this blog for eight years, generally twice a week and, while it’s been a lot of fun, I’m moving on. If you wish to browse through the past posts, please do so in the next few weeks, because the website will be shut down in June. If you would like to move on, too, to other language blogs, I would recommend:
https://www.merriam-webster.com
https://www.urbandictionary.com
https://www.worldwidewords.org
Bookmark these now, because this website will be shut down in June.
Thanks for reading it, and keep on having fun with words!
Rainforest Writer 
My heart sank when I read the title of this blog. I knew it was your “swan song” and final blog. I cannot tell you how much I have enjoyed being a recipient of your biweekly witty and informative email on words and so much more. I shall miss this enormously. I am deeply grateful to you and wish to thank you most sincerely.
Licette How
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Thank you! I’ve enjoyed writing the posts, not only because I love the language, but because readers like you enjoy reading them.
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I will miss your blog Lea. Thanks for all the linguistic explorations.
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Thank you very much for your contribution to our knowledge of word and phrase origins and wordplay! Your blog has been a treat with consistently interesting content, so very well-written and with a deft slice of humour as well. It’s helped many of us get through some dismal days these past two years especially, or at least that is true for me. A big thumbs up and may your next book be a smash hit, much like Rich Strike ran the Kentucky Derby yesterday!
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Thanks, Caroline! I’m happy to know I had some good effects!
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