Celebrating a career milestone is certainly not unusual for a lawyer. Partners who have globe-trotted, managed offices or built practices from the ground up clearly have plenty to be proud of.

But Chris Parsons wanted to mark 30 years at Herbert Smith Freehills with something different that was relevant to his time at the firm. His choice of party? 30 charity marathon-length walks across India in 30 days.

"India is an important part of what I do," says the country practice chair and corporate partner, who has been in the role for 10 years and lectures at a number of different universities in Bangalore, Calcutta and Delhi. "I'm here for a week or two weeks every month – it has become something of a second home to me.

"I wanted to mark the [30 years] by doing something not only for an India charity but in India rather than simply doing it in Europe or the UK. That's when I hatched this mad idea of 30 years, 30 marathons 30 days. I then decided: why don't I try to raise $1m? That might end up proving a bit ambitious but I thought I may as well aim big."

Unsurprisingly, this not the first time the 53 year-old father of four has jumped at the opportunity to take part in a physical challenge in the name of charity. Three years ago, shortly after his 50th birthday, Parsons cycled approximately 1000 miles with a friend from to London to Gilbrata, and prior to that rode his bike the length of Britain from Land's End to John O'Groats.

This is also the second time he has opted to support an Indian cause; namely, the Loomba Foundation, which supports widows and their children in India and countries around the world. He chose this particular charity after sitting next to Lord Raj Loomba at a dinner, whose own mother had been widowed and who had set up the organisation in recognition of his own lucky circumstances. "The story struck me as an important one," says Parsons. "He said if I did the [Gilbrata trip] for him he would meet me in Gilbrata, and he was true to his word."

Parsons – whose career has included time in Hong Kong, London and in Singapore where he was managing partner for South East Asia – admits that his upcoming expedition is not going to be an easy one. The route from the Gateway of India in South Mumbai to Bangalore is set to be long (1260km to be exact), hot and off-the beaten track, posing a significant physical challenge.

The plan is to walk rather than run, though evidently still with the gruelling task of hiking for 10 to 12 hours per day. "There are certain things I clearly cannot do" Parsons says, "and running 30 marathons in 30 days, I know for a fact that I cannot do. But I hope I will be able to walk it."

The good news is the $280,000 already raised by Parsons, not to mention a vast spread of beautiful scenery awaiting him. Having specifically chosen a coastal route, Parsons will take a road which winds around some of India's best beaches on the West of the country, before cutting inland to get to Bangalore across the Western Ghats mountain range. From tropical shorelines to lush rolling hills, famous for their biodiversity, Parsons should expect some fairly spectacular views. "This will take me through into Bangalore, I hope," he says, with a hint of anxiety.

Luckily, there is little chance of him getting lost, thanks to the help of a man called HV Kumar – dubbed "India's highway King" for his expertise on India's roads. Kumar, who has an online group with around 15,000 members interested in Indian trails, is also a source for Google maps – his knowledge of the local geography being second to none.

"He has designed the route and has also driven the route for me," Parsons explains, "and mapped out, on a very detailed basis, all of the little restaurants, petrol, chai (tea) and snack stops, and also identified the guest houses I'll be staying in." He adds that someone called Atul from the Loomba Foundation will take care of all the logistics. "Atul will be sorting out water, buying food, sorting out hotels, speaking to locals about the nearest stops, taking photos, doing videoing, liaising with local press, all of those sorts of things. My job will be to walk and he will do everything else."

Pepsi's Gatorade meanwhile will provide snacks and drinks to replenish salt and glucose levels, in addition a back-up driver who will carry supplies. A local hospital is providing a physiotherapist in the event of problems.

"Lots of people have said they'll join me for sections," says Parsons, "I hope they will. I think some people will join for the first day and maybe towards the end but whether they will join for other parts we'll need to see."

He concludes that although it's for a good cause, he is rather apprehensive about the journey. "I am looking forward to it but at the same time I'm also nervous. Luckily my son – who is 24 and doing sports' science – is great – he said look dad, the human body is capable of doing extraordinary things, so you will be surprised what you're capable of." More worrying might be the snakes…