Most workplaces have at least one sneaky, devious and snidey employee who wouldn't think twice about walking over one of his colleagues for personal gain or sadistic pleasure. By law of averages, you'll probably come across one of these individuals at some stage of your career. If and when it happens, don't just turn the other cheek and allow yourself to be screwed over. Your career could suffer if you allow a backstabber to take advantage or bully you.
Watch your tongue and remain on your guard whenever dealing with your backstabbing colleague. Avoid divulging any information about your personal life that could in any way be used against you or gossiped about. Don't make any remarks about other co-workers that could be considered off-colour and never unburden yourself of negative opinions relating to your employer's policies or practices when the individual in question is within earshot. Be especially vigilant when attending social occasions outside of work with your backstabbing co-worker, particularly if alcohol has been consumed.
Keep work-related ideas to yourself until you've presented them to one of your superiors. Your backstabbing colleague may be the type to pinch any plans you come up with and attempt to pass them of as his own. If you know your workplace foe is in the habit of extracting information from other staff members, watch how much you reveal whenever you're not in the company of people you know you can trust. When necessary, make it clear to co-workers you talk to that you don't want anything you say repeated to your backstabbing workmate.
Maintain a record of all dealings you have with the backstabber wherever possible. If you wouldn't put it past the person in question to engineer a situation with the sole aim of getting you into trouble, keep notes about any project you work on together. If you can, try to communicate solely by email so as you have documentary evidence of all exchanges between the two of you. When this isn't possible, involve a co-worker in work-related dealings you have with your untrustworthy colleague.
Calmly confront the backstabber about his behaviour. Explain that you're aware of what he's been doing and saying and ask him why he deems it necessary to carry on in such a manner. Tell him you find his conduct unprofessional and unacceptable. Say that you expect his behaviour to improve, and that if it doesn't, you'll be left with no option but to report him to your manager.
Report your backstabbing co-worker to your immediate superior. Present any evidence you have of his shabby behaviour and explain that you expect something to be done. Depending on the nature of the backstabbing, your colleague could be guilty of discrimination, harassment or bullying in the workplace. If your managers fail to adequately deal with your complaint and you feel as though you've been poorly treated, consider discussing your situation with a union representative or an employment solicitor.