Paul Rippon, who was also deputy chief executive at the business, said it had been a privilege to co-found the bank in 2015 but he was now running a farm in Northumberland with his wife.
In a post published to his LinkedIn page, the executive said: “Why did I leave? Simple, to go and enjoy life.
“At 48 years young I’ve been working in financial services for 27 years and working away from home for the last eight years.
“Building a fast growing bank takes its toll and even reducing my ‘work hours’ didn’t reduce the cognitive and emotional overhead.”
He explained that wife Debbie has taken the lead in building a family business, Barnacre Alpacas, and he is ready to get more involved.
Mr Rippon added: “With no farming background or experience we now have over 300 alpacas and welcome many visitors to our farm and holiday cottages.
“For the next few weeks and months I’m going to enjoy some time with Debbie at our wonderful farm in Northumberland.
“You’ll find me doing the feed rounds, hosting alpaca walk ‘n’ talks and driving my tractor.”
After April the banker said he plans to spend one day a week working as a consultant, coach and non-executive, with the rest of the time “reserved for Debbie, our alpaca farm and enjoying life”.
The banking veteran has worked throughout the sector, including NatWest, Northern Rock and Ireland’s AIB. Later, he joined another challenger bank, Starling Bank, before heading off to help found Monzo.
Since launching in 2015, Monzo is now valued at around £2 billion and is in the process of raising a further £100 million.