He tweeted: "Great that Prince Harry says counselled for grief & imminent breakdown. Hope lessens stigma of seeking help."
He later brought attention to how mental health services in the UK are underfunded, adding: "Also hope Prince Harry interview increases pressure for more NHS mental health resources, or indeed any in some cases".
Labour MP Chuka Umunna, who was only year older than Harry when his father died, also said he was touched by the interview.
He wrote on Twitter: "Big big respect to Prince Harry for opening up about his mental health and grief.
"Losing a parent so young is v.tough. I lost my Dad at 13 -doing so in the public eye wld have been harder still".
MP John Woodcock added: "Prince Harry opening up about the way he processed his grief will help a lot of people.'"
The prince's decision to speak out was also lauded as 'a true turning point' by mental health charity Mind, while campaign group Time to Change said he 'will have helped change attitudes' by sharing his experiences.
Paul Farmer, chief executive of mental health charity Mind, described Harry's interview as "inspiring".
"It shows how far we have come in changing public attitudes to mental health that someone so high-profile can open up about something so difficult and personal," he said.
"We know that this will have a huge impact on people who are still struggling in silence with their mental health - every time someone in the public eye speaks up we know that it encourages ordinary members of the public to do the same."
He hailed the interview as a "true turning points", adding: "As a society we must no longer adopt a 'stiff upper lip' attitude."
Sue Baker, director of Time to Change, said: "Prince Harry sharing his experiences of mental health issues and the counselling he sought as a result of losing his mother will have helped change attitudes, not just at home but also overseas.
"It was a dream of mine 20 years ago that we'd see the royal family join sports people, music stars, politicians and business leaders as well as everyday people in sharing their mental health experiences in all sorts of communities."
Prince Harry, who is spearheading the Heads Together mental health campaign alongside the Duke and Duchess of Cambridge, admitted that shutting down his emotions after losing his mother had 'a quite serious effect on not only my personal life but my work as well'.
He told the Daily Telegraph: "My way of dealing with it was sticking my head in the sand, refusing to ever think about my mum, because why would that help?
"(I thought) it's only going to make you sad, it's not going to bring her back. So from an emotional side, I was like 'right, don't ever let your emotions be part of anything'.
"So I was a typical 20, 25, 28-year-old running around going 'life is great', or 'life is fine' and that was exactly it.
"And then (I) started to have a few conversations and actually all of a sudden, all of this grief that I have never processed started to come to the forefront and I was like, there is actually a lot of stuff here that I need to deal with."
The prince said he eventually sought help after his brother told him he needed to deal with his feelings. He told how boxing "saved" him by helping him deal with aggression after he came close to "punching someone" when he was 28.
"It was 20 years of not thinking about it and two years of total chaos," he explained.
Asked whether he had ever been to see a "shrink", he replied: "I've done that a couple of times, more than a couple of times, but it's great."
But the prince said that he was now in a "good place" because of the "process I have been through over the past two and a half years".
"I've now been able to take my work seriously, been able to take my private life seriously as well, and been able to put blood, sweat and tears into the things that really make a difference and things that I think will make a difference to everybody else," he said.
Heads Together, an umbrella organisation for mental health charities, is the London Marathon's charity of the year.
The Duke and Duchess of Cambridge and Harry, who hope the race will be known as "the mental health marathon", will hand out medals on the finish line at the Mall on Sunday.
Harry will also open the London Marathon expo at the ExCel Centre in east London on Wednesday, where 39,000 runners will register ahead of the event.
Bryony Gordon, who interviewed the prince for the Daily Telegraph, has previously spoken of her struggles with bulimia and obsessive compulsive disorder and is running the 26.2-mile course for the campaign.
Harry's interview comes amid calls for mental health education to be made compulsory in schools.
An open letter to The Times, organised by Lauren Callaghan, co-founder of the Shaw Mind Foundation, said mental health should be valued alongside academic achievement in schools.
The letter, signed by more than a dozen clinical psychologists and psychiatrists, states: "Schooling focuses on physical and academic education but neglects mental wellbeing.
"By educating young people about mental health and wellbeing in school, we can increase resilience and coping skills, boost awareness of mental health issues and encourage open, honest discussions about mental health."
Where to get help:
• Lifeline: 0800 543 354 (available 24/7)
• Suicide Crisis Helpline: 0508 828 865 (0508 TAUTOKO) (available 24/7)
• Youthline: 0800 376 633
• Kidsline: 0800 543 754 (available 24/7)
• Whatsup: 0800 942 8787 (1pm to 11pm)
• Depression helpline: 0800 111 757 (available 24/7)
• Rainbow Youth: (09) 376 4155
• Samaritans 0800 726 666
• If it is an emergency and you feel like you or someone else is at risk, call 111.
