Mazer Rackham won the Second Invasion for humanity, and it's been said by some sources that he is half Māori. Is there any other information about Mazer Rackham's experiences and origins prior to his introduction in Ender's Game?
Yes. There's a prequel trilogy by Orson Scott Card and Aaron Johnston covering the events of the First Invasion:
"Earth Unaware" which features an as-yet-unimportant New Zealand Special forces Lieutenant Mazer Rakham in a bit part.
It has interesting scene of how he endured an hour long torture no human was expected to endure via some sort of Maori meditation; and his being rejected from Earth-wide Special Forces because he chose to endure the torture test instead of breaking out of it. A second scene is of Mazer taking a part in more martial test for that position, showing his out of the box thinking.
"Earth Afire" about the very first Bugger attack, which feature's Mazer's heroics in fighting the First Formic War including blowing up one of the Formics' 3 landers in China (though his participation there was not mentioned in Ender's Game) as well as details about his origins and background (some of which I cited in this answer on SFF so won't copy/paste here).
As seems typical of Mazer, the whole heroics is against (bad) orders and getting him arrested etc (from Mazer in Prison we learn that his attack on Formic Queen that defeated the Second Invasion was also against orders).
"Earth Awakens" - Centers on Mazer's team effort to take out the Buggers' mothership. It ends with Mazer accepting the offer from the first Hegemon/Strategos to join the post-invasion just formed IF.
UPDATE: as per Aaron Johnston's tweet, there will be a follow-on series, most likely about the Second Formic War, culminating with Mazer killing the invading Queen's ship and winning it.
There's a short story, Mazer in Prizon, that appeared in Orson Scott Card's Intergalatic Medicine Show magazine Issue 1. It covers the time after Mazer saved Earth in the second invasion and before Ender's Game begins.
There are a series of comics (published by Marvel) that cover the first Formic wars, Formic Wars: Burning Earth, and Formic Wars: Silent Strike. These introduce the young Mazer and tell most of his backstory. Burning Earth isn't really about Mazer, but Silent Strike does focus on him (as well as continuing some of the Burning Earth story). The impression reading Silent Strike is that there will be a further series (or that that was the original plan) that would again focus more on Mazer, as he becomes more central to the defence, and eventually is the key to winning the war.