Ahead of their 150th anniversary next season, the West London club is offering investors a 5.5 per cent annual return, paid semi-annually, over an initial five-year fixed term.
The bond, which could be raised to £15m if there's sufficient demand, will be used to improve the club's rugby infrastructure, stadium facilities and global presence - specifically in the USA, where Harlequins are planning to play pre-season fixtures over the next four years.
A new director of rugby to replace the departing Conor O'Shea, who joins Italy at the end of the season, will also arrive this summer to aid the club's growth plans.
"What we’re doing with the bond is trying to build the next chapter over next season and the next five seasons and we will have a new director of rugby to help us on that path - the [recruitment] process is going well," chief executive David Ellis told City A.M.
"You’ve always got to keep ahead. We’re so competitive in the Premiership, there’s almost nothing between us. It's one of the most competitively balanced leagues in the world.
"You have to keep improving, building on what you have and you have to keep investing so that’s exactly what we’re trying to achieve."
Harlequins also highlight the current rude health of rugby both at home and abroad as ripe for their plans for growth.
"We’re in a great place on and off the field but we have a strategy to build and grow and deepen our supporter base around the world," said Ellis.
"The big picture is rugby is in great shape, as a professional sport with the World Cup being in England, it has meant a massive growth in attendance, a massive growth in engagement. It’s put a whole load of new money back into the sport."
"That’s what this bond is about, it’s about helping us develop our rugby core, to engage with a bigger supporter base and engage with the wider audience around the world."
Investments in the bond, for which applications will close on 16 May, can be made in £1,000 multiples with minimum investments are set at £2,000.
Any applicant will be invited to join the Quins' Quarters Club, which offers members the chance to attend events with the players and staff.
" This is an opportunity to get closer to the club, to understand more about what we do, to be a part of that next journey," said Ellis.