Passion Capital has already committed £5m. The company had earlier invested £2m in Mondo last year.
The new funding will allow Mondo to start its public launch with an accelerated roll-out of its services. The bank is awaiting regulatory approval for its UK banking licence.
It is the second round of fundraising for Mondo as it seeks the capital it requires to launch publicly later this year.
It will reserve £1m of the fundraise exclusively for everyday investors through the crowdfunding platform Crowdcube on 1 March 2016.
Mondo founder Tom Blomfield said: "Early on, we decided that openness and transparency was the only way to ensure that Mondo was solving real customer problems.
"Our early users have helped us shape the bank as it’s grown and we’re enormously grateful for their help. Now we want to give them a chance to own part of the bank that they’ve helped to build."
Apart from owning shares in the bank, investors will also get a Mondo Investor Mastercard Prepaid Debit card and access to the Mondo iPhone app.
