The leaders of the B.C. NDP and Green parties have reached an agreement designed to remove the long-governing Liberals from power.

On Monday, John Horgan and Andrew Weaver announced their intention to use their parties' combined 44 seats in the provincial legislature to end Christy Clark's reign as premier and form an NDP minority government.

"I am very excited about the prospect of delivering for the people of British Columbia what they voted for on May 9, and that was change," Horgan said.

"We can do great things when we work together. We can do great things across party lines when we have a government in place that's anxious to do that."

Their announcement ends weeks of speculation that began after the election left Weaver and two other Green MLAs holding the balance of power, and ramped up significantly after the results were finalized by Elections B.C. last week.

Few details of the NDP and Greens' plans have been shared yet, but the parties did confirm the agreement does not involve forming a coalition.

Weaver said it's important to demonstrate a minority government can operate stably for a full four-year term. Should the NDP and Greens enact voting reform, which Weaver repeatedly called a top priority during negotiations, minorities could become the norm.

"We wanted to maintain a minority situation to show British Columbians that it can work," Weaver said.

The deal has already been ratified by the three Green MLAs and will be presented to the NDP caucus on Tuesday. Horgan said the details will be shared with the public after the plan is approved, and the parties will then bring it to B.C.'s Lieutenant Governor, Judith Guichon.

It's unclear how Clark will respond. She remains premier for the time being, and can choose to attempt to pass a confidence vote in the legislature, resign, or ask Guichon to dissolve the government and call another election.

"We have the majority support of members in the legislature and that will be up to the premier and the Lieutenant Governor to discuss," Horgan said.

Clark issued a brief statement shortly after the NDP and Greens' announcement but offered little insight into her intentions.

"As the incumbent government, and the party with the most seats in the legislature, we have a responsibility to carefully consider our next steps. I will consult on those steps with the newly elected BC Liberal caucus, and have more to say tomorrow," Clark said.

She also suggested the yet-undisclosed agreement between the NDP and Greens "could have far-reaching consequences for our province's future."

Weaver spent days negotiating with both parties before finally deciding to back the NDP. Up until Monday, his public statements suggested the Greens could have sided with either, despite polling that showed a majority of his supporters favoured a deal with Horgan.

"We spent four sessions with the B.C. NDP – many, many, many hours talking about issues about commonality, talking about differences. We also had good negotiations with the B.C. Liberals, and what was obvious to us, the B.C. Greens, is that there is so much commonality in this legislature," Weaver said.

"In the end we had to make a difficult decision, a decision that we felt was in the best interests of British Columbia today."