What is the ruling in Islam on a friend seizing a job opportunity by negotiating directly with the company without the knowledge of the person who was going to be employed, and is his action considered betrayal and usurpation of livelihood?

If an agreement and satisfaction have been reached between you and the employers regarding your employment with them, then it is impermissible for your friend to obtain the job for himself if it is designated for one person, due to the Prophet’s (peace be upon him) saying: "None of you should sell over the sale of his brother, nor propose over the proposal of his brother, nor bid over the bid of his brother."

This action by the friend is considered a betrayal of his friend who trusted him, and in the Hadith: "It is a great betrayal that you speak a word to your brother that he believes you in, while you are lying to him."

However, if no agreement was reached between you and the employers, or if the job was for more than one person, then there is no harm in his action. His argument is valid, but he incurs sin by using an unlawful means.