But behind closed doors his family and his marriage were suffering. So he gave it all up, and launched a personal crusade helping to save other peoples' marriages.
The change brought a mixed response from his peers. 'My partners in the practice were kind and supportive. Other people tended to say, 'That's nice' - which meant they thought I must have been loopy.'
The charity Rob founded is CARE for the Family, and today, as its executive director, he travels throughout the UK and abroad, giving seminars about marriage and the family.
Whether you call it preaching, or marriage guidance counselling on a mass scale, he is certainly packing them in. Sometimes he has audiences of up to 1,000 people.
He has talked in Dublin and Paris, even to a hall full of military personnel at Space City in Russia. He and his wife, Dianne, have produced a video - and then there's his book, Loving against the Odds, published last month.
It all began with a crisis in his own 23-year marriage. Rob, a 45-year-old Welshman, has the demeanour of one of those men on daytime-television sofas. He is clean-cut, quietly spoken and considerers each question carefully before answering. He and Dianne share a big house in suburban Cardiff with their son, Lloyd, 13, daughter Katie, 16 - and a 48-year- old dustman called Ronnie.
Ronnie's been with us about 17 years,' Rob says. 'He was living in appalling circumstances, and Dianne invited him to come and spend Christmas with us. He stayed that night, and he never left us. He's been there longer than the children. They regard Ronnie as a mixture of a brother and an uncle.'
The Parsons' troubles began just after Lloyd was born. Dianne became ill with what was thought to be a depressive illness, but later found to be ME, or chronic fatigue syndrome, and it threw their lives into turmoil.
'My dad was a postman, mum was a cleaner,' says Rob. 'We didn't have running hot water, inside toilet, none of that stuff. So when I got into law, for me it was a whole new world. And then I began to be very successful.
'I was incredibly busy, running lots of agendas. Then, when Dianne became ill, she woke up one day and said, 'I just can't cope any more.' It made me to re-evaluate lots of things.
'I always used to be able to fix things. But I could do nothing about this. I felt totally helpless. I wasn't used to feeling like that. I think at the beginning, too, I also felt quite angry with Dianne. She would be well for a while, then she'd become ill again.'
The illness continued for about two years. The experience made him look closely at his working life and how it affected the family. 'I would come home. Di would have loved to speak to me, but had long since given up. The two little children hadn't.
'Lloyd would say, 'Dad, I'm in the football team on Saturday.' Kate would say, 'Susan pulled my hair again.' But I'd be distant until the telephone rang. My little boy would say, 'Dad, it's for you.' And suddenly I'd come alive. The message I was giving to my family was, 'This is what matters to him.'
'I think I was brought to my senses in the nick of time. While Katie and Lloyd were growing up, I was at least thinking about these kinds of issues. I almost remember the day I realised the door of childhood closes so fast.'
Rob's lifestyle often made Dianne feel she was living in his shadow. 'There were times when I was very frustrated,' she says. 'Tea would be on the table, Rob would be late from work, and even then the phone was a constant interruption. Quite a few times I would get, 'Oh, you're Rob Parsons' wife, aren't you.' There came a day when I found that extremely difficult to handle. But part of it is what society makes of motherhood - that it isn't an important job.'
Rob and Dianne were heavily involved in their local church. They began organising meetings at home, sharing their own marriage problems with others. 'We found that, as we shared our times of apparent failure, it gave people hope again because they could identify with us,' he says.
It made them both want to work with families. Dianne says: 'I told Rob I really felt that, if ever I did feel well again, I would like to work with young couples. I found it tough being the mum of two toddlers. I felt I had something to share with young mums who were going through the same situation. 'So when Rob said that the time had come for him to leave law, I wasn't aghast.'
He wound down his involvement in the law practice, and in 1988 founded CARE for the Family. He gets no salary, so he does occasional legal consultancy work.
'I can't say it was a great financial sacrifice, because we had, by any standards, enough,' he says. 'To be honest, it had more to do with ego than finance.
'One minute, I was senior partner with this large law practice with 10 offices; I'd go in and say, 'Make me a cup of coffee,' and they did. And the next, I was in this little office, having to find my own stamps and rubber bands, and I'd ring people up who wouldn't return my calls.'
At one of his first speaking engagements, Dianne asked if she could come along and address the audience, too. 'She'd never spoken in public before,' says Rob. 'But she stood up - and here was this brilliant communicator. People were moved.'
Then they began to present their 'Marriage Matters' seminars together. Much of the Parsons' message is told in anecdotes, funny stories and examples from their own lives.
'We began to have lots of letters coming in to us,' says Rob. 'From people who wanted help in various ways.
'One thing we found we could do was break the sense of isolation. Many people going through marriage break- ups believe they're the only people going through it. It's very common for one partner to imagine the death of their partner.
'Gosh, if my partner died, the new freedom I'd have, this magical new person I'd meet. When you say this to a couple of hundred people, first of all you see looks of shock, then wry amusement as they realise they're not the only ones who've felt it.'
Dianne, 44, says Rob's change of career has altered their family relationships, and the way she perceives herself. 'Before, I felt very much inadequate. Now I have a role. And I feel I've got a lot to offer women in the same situation. There are a lot of people really hurting out there. I really feel I'm able to get alongside them and say, 'I understand.' '
'Loving against the Odds', by Rob Parsons, is published by Hodder & Stoughton, pounds 5.99.
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