"What we've done is capture the move of our younger people to an internet future and we wanted to make sure we were part of that future and one of the ways to do that was to buddy up to an organisation that already understands that world," Mr Harawira said.
Ms Bradford, who had threatened to leave if the deal went ahead, said she tendered her resignation as soon as she saw Mana' press release confirming it.
"Sucking up to a German millionaire is not my vision of the future and I think Mana has made a big mistake ... in the long run, it's lost what I joined it for which was that sense of integrity."
But Mr Harawira said polls he'd seen "actually suggest that Mana members are entirely favourable with it".
The next step for the joint party is the announcement of the Internet Party's leader tomorrow in Auckland.
Mr Harawira said once it became clear who was in the frame for the job, "it made it easier for us to continue the negotiations".
Labour leader David Cunliffe said his party, "will be interested to see how that romance works out over time".
With the joint party seeking support from young disengaged voters rather than cannibalising the vote on the left, the Herald understands Labour has given some thought to pulling its punches in Te Tai Tokerau to give the alliance a better chance of bringing in additional left-block MPs. But Mr Cunliffe said Labour's Te Tai Tokerau candidate, Kelvin Davis, would be running hard to win the seat.
Maori Party president Rangimarie Naida Glavish said Labour "owes it to Maori voters to clarify" whether it would advise its supporters in Te Tai Tokerau to switch their electorate votes from Mr Davis to Mr Harawira.
Prime Minister John Key said the alliance was about Mr Dotcom putting money behind a political party in a bid to block his extradition to the US.
"I find that pretty odd but if people want to vote for that, they are welcome to do it, but in the end everybody knows that if you vote that way, you are voting for a left-wing party."
Mr Harawira said Mr Dotcom's looming extradition hearing and whether Mana would support his efforts to remain in New Zealand had "not even come up once" during discussions over the past few weeks.
How it works
• Mana and the Internet parties will run a joint list vote campaign but have independent electorate campaigns under their own names.
• Any electorate seats won by either party will count against the total the joint entity would be entitled to on the basis of its party vote.