Actually this word consists of two individual characters "将" and "由". "将" is future tense which means "will", "be going to", and "由" is used as a preposition "by" or "from". When using "由" the whole sentence is actually translated into passive voice. The real order of this sentence is "10月以后公司领导将由张华担任"(The leader of the company will be assumed by ZhangHua after October), and the real subject is "公司领导". It's the same as "公司领导将被张华担任"(but this is not used in Chinese). "由某人做某事" 相当于 "某事被某人做". That's why Chinese is so confusing!

‘将由’ 意思是，“将要 由”的省略。意思是 10月以后，将要由某某某担任公司领导。

将由 is two words,将means flew days later,由According to the passive.

Something will be done by someone

有点即将的意思， 公司领导将由张华担任，