"A lot of what I talk about in the book people don't get to hear," says the Sydney-based Wests Tigers star, who turned 27 last month.
"In Australia a lot of the guys are too scared to say anything. If you put your emotions out there, in the open, you get judged."
The book, he says, is "about me and how I feel, what it's like to be me". Apparently being him isn't all it's cracked up to be.
Though not complaining about his success, he struggles with the fact that wherever he goes in Australia he is accosted by fans wanting an autograph, a word, a photo - and in some cases, just to bait him. If you don't oblige the Aussie fans, he says, they're quick to turn on you.
"Fans think they know me but they don't. To the public I want to look confident and in control and everything - but we're human beings."
It's very different back in New Zealand. Here, Marshall says, the fans are more respectful, not so bold, which means he can just relax, be himself and chill with the whanau.
Many of his family members have followed him to Australia, but back in the Eastern Bay of Plenty he stays with his "other mum", Annalie Doherty, who still spoils him rotten.
There's always a meal on the table when he arrives, breakfast ready when he gets up, his bed made and washing done for him and the cupboards stocked with Toffee Pops. He clearly enjoys the fuss and happily admits he's always been a mummy's boy, lucky enough to have two mothers - his birth mum Lydia, a solo parent who had him when she was young, and Annalie, who, with husband Michael, took him in and loved him as their own.
Michael Doherty passed away in 2009 but left a huge impression on Marshall, grateful for the advice and life lessons his beloved "Dad" passed on.
Marshall was sent to Australia as a teenager when Lydia became concerned he might he headed for the wrong side of the tracks.
He made an impression immediately when he took the field for Keebra Park and was picked up by the Tigers from there.
He'd played many different sports growing up and learned his trademark "step" on the footpaths of Whakatane, dodging prams and pedestrians.
"I was always the smallest, skinniest, slowest kid, picked last for school sports and learned to step so I could beat the bigger kids." A loyal member of the Wests Tigers since debuting for them in 2003, the five-eighth realised a dream when he won the prestigious Golden Boot in 2010, awarded each year to the game's best international player.
Having come back from three shoulder reconstructions and captaining New Zealand to a Four Nations victory, it was a "pretty special" accolade.
If you want to upset Marshall, call him injury-prone, a label he came to despise following a recurring shoulder injury and one which dented his confidence.
"As much as people say something doesn't affect you, of course it does."
There's no lack of confidence now, however, and Marshall is driven by success.
In the past three years he's missed just two games.
"I did the hard yards to get back," he says. "All I was ever told was what I couldn't or wouldn't be able to do - when someone tells me that, it just makes me want to do it even more."
Marshall says he's more than fancy sidesteps and flick passes and isn't as instinctive a player as people may think.
Those flick passes are practised over and over and, for him, a solid game isn't about fancy footwork, it's about being able to control the team to win the game.
Marshall reckons the best is "definitely" yet to come.
"I'm not satisfied that I've done enough yet - I think I can learn a lot more and be a lot better ... A lot of guys don't play their best until their late 20s, hopefully I'm getting there."
Title: Benji - My Story
Author: Benji Marshall with Glenn Jackson,
Publisher: Hodder Moa, $44.95