A good answer to this question requires a brief explanation of the literal meaning of the following words: qadha (decree), qadar (destiny), taqdir (predestination/determination), and taqdire-elahi (divine determination).

“Qadar” literally means size, “taqdir” means measurement and the definition of “qadha’” is execution and completion.  But in technical terms, taqdire-elahi (divine determination) is used for Allah’s determination regarding the limits and boundaries of different phenomena and all of the traits and characteristics of His creatures that all have their own specific cause in this world.  The concept of Qazaye-elahi (Gods decree) refers to the completion and creation of creatures at the final stage.  In other words, when all material conditions for the taking place of a phenomenon are met, He is the one who “verifies” it and allows it to take place, and to put it simply, “finishes the job”.   Of course, it should be noted that when it comes to our actions, [which are part of the different phenomena this world consists of], Allah’s (swt) divine decree covers them with all of their causes and characteristics, one of those causes being our choice and free will.  So what Allah (swt) allows to take place when it comes to our actions, is what we have chosen to do.  Therefore, considering the fact that the attribute of free will is a part of what He determines as a whole, there is no contradiction whatsoever between attempting suicide and decree and destiny.

However such a person’s position in the hereafter depends on the conditions of how he committed suicide. For example if his type of attempt was a type of attempt that would usually and most likely end in his death, it would be considered suicide and according to the traditions would have a severe punishment.  On the other hand, if what he did was something that usually doesn’t lead to death, yet he died of it, he won't have such a punishment and if he is to be punished, it will be much less.