The Qur'an isn't a great source for Muhammad's life, since there are very few direct mentions of the Prophet within the text. Muhammad did exist, as we have several documents written in the 630s and 640s referencing him. The first is a Christian anti-Jewish pamphlet (supposedly) written in Africa in 634, which claimed that some Jews were convinced by the rise of a new unnamed prophet amongst the Saracens (Arabs) as a portent of a new Messiah. The second is a short note written on a Syriac Gospel book around 636, presumably written by a monk writing down the momentous events he just experienced. The most important line is:

... many villages were ruined with killing by [the Arabs of] Muhammad and a great number of people were killed and captives [were taken] from Galilee as far as Beth

This note however is faded and the reading uncertain, so Robert Hoyland, a historian who basically wrote a book covering all the sources for early Islam, prefers a chronicler's account written around 640 as the 'first' mention of Muhammad, which said that:

In the year 945, indiction 7, on Friday 4 February (634) at the ninth hour, there was a battle between the Romans and the Arabs of Muhammad

These sources don't really tell us much about what Muhammad did, but he was clearly an important figure to the Arab armies invading Palestine, so he definitely was a person of political and religious significance. A bit later in the 660s we have a much more detailed account from a reasonably reliable Armenian historian now called Pseudo-Sebeos:

At that time a certain man from among those same sons of Ishmael whose name was Mahmet, a merchant, as if by God’s command appeared to them as a preacher [and] the path of truth. He taught them to recognize the God of Abraham, especially because he was learned and informed in the history of Moses. Now because the command was from on high, at a single order they all came together in unity of religion. Abandoning their vain cults, they turned to the living God who had appeared to their father Abraham. So Mahmet legislated for them: not to eat carrion, not to drink wine, not to speak falsely, and not to engage in fornication.

He said: ‘With an oath God promised this land to Abraham and his seed after him for ever. And he brought about as he promised during that time while he loved Israel. But now you are the sons of Abraham, and God is accomplishing his promise to Abraham and his seed for you. Love sincerely only the God of Abraham, and go and seize your land which God gave to your father Abraham. No one will be able to resist you in battle, because God is with you.'

There are other much later Muslim sources from the late eighth/early ninth centuries, but in broad terms they match up with the contemporary evidence - that Muhammad was a merchant, that he preached a new religious doctrine and that he led his followers on raids. The details of his life is often debated, such as whether he personally led campaigns into Palestine or if his religious movement was an ecumenical one inclusive of Christians and Jews, but I see no reason to question the general outline of the traditional biographies of Muhammad.

I'm not qualified at all to answer this, but I'll say it before someone else does. Can you please specify? Just asking what we really know about his life, isn't enough to get solid answers.