According to Plagiarism.org,

copying so many words or ideas from a source that it makes up the majority of your work, whether you give credit or not

is considered plagiarism.

Now let's say that I am writing a novel about a certain person's life and everything that this novel is based on is the events as described in the person's journal. Note that I will not be copying the journal word for word, but will instead only be using the facts and events as described in the journal as the primary and most probably the only source of my novel.

Is this considered plagiarism? If so, is there a way to get around it?

According to Plagiarism.org,

copying so many words or ideas from a source that it makes up the majority of your work, whether you give credit or not

is considered plagiarism.

Now let's say that I am writing a novel about a certain person's life and everything that this novel is based on is the events as described in the person's journal. Note that I will not be copying the journal word for word, but will instead only be using the facts and events as described in the journal as the primary and most probably the only source of my novel.

Is this considered plagiarism? If so, is there a way to get around it?

Info based on a previous answer:

Well see, it will actually be a novel as I am not writing a factual account of the person's life, but in fact a fictional story based on the given facts. The journal given is merely an explanation of the events and listed facts while my novel will be in the form of a fictional story. Also, the journal was written in the 18th century, some 250 years ago, meaning that I cannot ask for their permission.