Robert Mitchum did not receive an Oscar nomination for portraying Jeff Bailey in Out of the Past.
At the beginning of this film we meet Michum's Jeff who is just a gas station owner in an unassuming town who is going out with a local girl and just apparently content with this small town life. Mitchum is convincing enough at being just a man enjoying this life, but he also of course shows that there is much more to him found in history. Quickly though Jeff tells of his past in which he was a private detective working for a shady man named Whit Sterling (Kirk Douglas) who hires him to find his girlfriend Kathie Moffat (Jane Greer) who he claims shot him and stole 40,000 dollars from him.
Jeff quickly finds Kathie but finds that he is quickly drawn to her, and hesitates in informing his employer. Mitchum is good here in showing the Jeff of the past who seems happier and quite invested in this relationship. This is not some sort of big romance that seems larger than life by any means, but there is some connection there between them. Mitchum does not portray this as really Jeff love of his life, but something he can't help but fall into here as it just seems something so natural and easy to do. Mitchum makes it a bit more of circumstance than of unending passion.
When first confronted of this situation in this past scene Mitchum does not have a particular calm and cool here that works well in showing really that at this time Jeff has not learned to handle such situations. When he lies to Whit about Kathie there is an uncertainty in him that Mitchum portrays as Jeff not being entirely in his element here. Mitchum usually is an actor who cannot be messed with by anyone due to his remarkably strong presence, but early on he effectively makes Jeff not entirely capable of maneuvering within the twists and turns of the noir world.
Mitchum's usual presence though does come out as we see Jeff after has had his own problems due to a double cross and the results from that. When he gets back involved in the plot Mitchum shows Jeff quite differently as he becomes extremely cynical in his portrayal. Jeff does not seem to care about what is going on, and seems very embittered by the whole affair now, and Mitchum world weary face fits this attitude perfectly. Mitchum makes it clear that Jeff only really is now involved with the whole thing because he is in too deep from before.
Mitchum effectively conveys this sad state of Jeff for the rest of the film, but at the same he also bring about the change of Jeff's abilities within the world. He has learned from his experience and Mitchum commands most of the rest of the film. When Mitchum takes over he really takes over, and he does not leave a question to Jeff abilities to maneuver through the plot. Mitchum shows a great intelligence in his performance convincing that Jeff would be able to be the man in charge, even though all the while he still is in a rock and a hard place due to what happened in the past.
If I were to have a complaint, and I really don't, the film has moments where they proclaim that Jeff is in some way bad. There really is not anything that really would say that he is in any way a troublesome man, but this is just a minor flaw in the film that really with Mitchum's portrayal. Mitchum really is very strong in the role, and he is a great noir hero who is easy to follow through his sad journey. I won't say that this is Mitchum's greatest performance by any means, but it is an effective performance which spotlights his unique screen persona very well.