His first challenge will be tomorrow's inaugural Twin Lakes Marathon between Lake Hawea and Lake Wanaka.
Until next Sunday, Law (50) will run an average of 51.4km per day through some of New Zealand's most remote and beautiful country, with the goal of covering a total of 360km.
It is the second time Law has attempted such a mission. His first 7 in 7 Challenge in 2009 to run all New Zealand's Great Walks raised $85,000 and already he has raised $102,000 towards this year's goal.
Law stopped training two weeks ago - he has run more than 7000km in two years - and has been a bundle of anxiousness ever since.
"There is not much I can do that can help me now except rest and relax. I always get a nervous patch because I've done almost nothing for two weeks to get rested. I am starting to fret that maybe I am not fit enough or will get injured. All the usual irrational stuff. But I know from personal experience you always go better if you feel this way than if you say, 'Yay! I am so trained up!'," he said on Thursday.
Law is most apprehensive about the weather, worried he may suffer in the heat, particularly on the Motatapu Track between Wanaka and Arrowtown on Tuesday.
To calm himself, Law has been "quietly" walking Mt Iron and pulling together the final logistics of his challenge.
His wife Sally, son Beinn and several friends will provide daily support and 120 runners have signed up to run one or more of next week's seven marathons with him.
At least 36 runners are from Auckland, with a handful travelling from the United States, Australia, Singapore and Hong Kong.
World multisport champion Richard Ussher, of Nelson, is also supporting the event.
Law's progress will be tracked by satellite during the event, with regular daily updates downloaded on to the 7 in 7 Challenge website.
Law will also be at Mitre 10's charity auction in Wanaka from 5.30pm on Saturday, which will be attended by television personality and former All Black Marc Ellis, who is running the Twin Lakes Marathon.
Wanaka Mitre 10 will have staff running alongside Law every day of the challenge and have set themselves a target of $10,000.
"I think by the end of this week, it will be a bit of a moving circus ... it will be quite an entourage by the end. It will be amazing," Law said.
THE HURT LIST
Mal Law's daily challenges are:
• Sunday, November 28: Twin Lakes Marathon (42.2km).
• Monday, November 29: Young-Wilkin Circuit (55km).
• Tuesday, November 30: Motatapu Gold (49km).
• Wednesday, December 1: Wakatipu Wonderland (38km).
• Thursday, December 2: Rees-Dart circuit (61km).
• Friday, December 3: Greenstone-Mavora Walkway (52km).
• Saturday, December 4: Kepler Challenge (60km).
