This is essentially how biography should be written, with a couple of major caveats. The thoroughness of the recounting of Proust's life, combined with Tadié's in-depth knowledge of the literary aspects of the works is profound. He knows not only "what happened," he is able to piece together a number of connections which would be absolutely unknown to the average reader. Further, he understands the place of other writers and acquaintances of Proust in relation to Proust's literary legacy.
This is why the first caveat is so surprising. When the book ends, we are left with Proust dead in his bed, being photographed by Man Ray. But I was hoping and expecting to see a summary or assessment of the impact and place of Proust in the literary canon, given all that we had absorbed in the previous 800 pages. But there was no such assessment. Perhaps Tadié expects his readers to glean this understanding from the whole, and if we have not synthesized a clear understanding of Proust's place in literature by this point in his biography, he is not about to do the synthesizing for us.
The other aspect that surprised me is that while there is obviously a detailed accounting of the compilation of RTP over the many years Proust wrote it, there is never a clear image of where, when and how Proust did his writing. He wrote in bed? What materials did he use? Did he write for hours at a time, or in snippets? Did he always follow a routine, or did he work impulsively. I just never felt I understood the episodes in which the dozens of notebooks were filled.
A final comment. It would be nice to have a brief explanation of the steps leading to the publication of a book at that time. From manuscript, to typescript, to galleys, to printer's proofs – I don't totally understand the implications of Proust making last-minute changes and how the editors, publishers and printers would have responded to that.
Overall, I'm glad I read this book with two volumes of RTP (out of seven, total) remaining to read. It will help me understand "who's who" and why. I recommend reading this biography while mid-stream in RTP. If you read it first, the references to scenes and characters will lack meaning. If you read it after, you'll wish you had known some of these things in advance....So read it in the middle of reading RTP.