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Sartre’s Existentialism and Marxism

So, Sartre was one of the first philosophers I ever read, and I still adore a lot of his work. However over the past year I’ve been going through a little Marxist phase and going to campus reading groups and events and things of that nature. I now feel decently well grounded in both Sartre’s Existentialism and Marxism, although notably I haven’t read later Sartre. I have heard as he got older he adopted more Marxist views into his philosophy. 

That turn Sartre took seems very strange to me, because I would have thought that Marxism and Existentialism were incompatible, as Sartre spent a good bit of time rebutting Marxist critiques of Existentialism in Existentialism Is A Humanism. I was under the impression that Marxists would scoff at some of Sartre’s ideas about human freedom and agency, and that Sartre could never reconcile himself to Marxism’s rigidity.

So, I was hoping this sub could help explain Sartre’s turn towards Marxism, as well as in what ways he reconciled it with his Existentialism, and what the reaction to this has been from Marxists and other philosophical schools?

Now, I know the answer to my question is probably just “read later Sartre”, but I’m busy right now and have more time for Reddit comments. I definitely plan on reading his later works in the summer, so I’d love recommendations for what to buy as well as any insights you guys have!
gpt
When Sartre was alive, Marxism (or a plurality of its adherents) was far more rigid and deterministic than it is today. The fact that Sartre tried to reconcile existential phenomenology with Marxism shows he saw himself as a kind of Marxist - just one at odds with his peers.  

Sartre's leftism is indebted to the famous Marx quote of *"Men make their own history, but they do not make it as they please; they do not make it under self-selected circumstances, but under circumstances existing already, given and transmitted from the past."* He is particularly concerned with the "*making"* as a verb. Marxism provides the field of opportunities to an agent but doesn't explain the radical particularity of any one choice. 

The most clarifying comment from Sartre to me about his Marxism comes from his late career writings (A Search for Method and Critique of Dialectical Reason) where he says something like *"Existentialism would have no reason to exist if Marxism ever abandons its teleology."*  Sartre wanted a Marxism that explained and reinforced human agency in a world that is fundamentally ambiguous.