Just last fall, the 54-year-old Horgan said he wasn't entering the race because he wanted younger leaders to step forward.
"I said a lot of things in the fall," Horgan told the media.
He formally entered the contest last month, saying many of those young New Democrats like MLA's Michelle Mungall and David Eby were urging him to run.
"I said I didn't want to see divisiveness and Mike and I have agreed that in the best interests of the party we unite today so that we can focus like a laser on (Premier) Christy Clark and the Liberals."
Farnworth, the NDP's finance critic, former cabinet minister from the 1990s and strong runner-up in the party's 2011 leadership race, announced he was ending his leadership bid and joining Horgan's team.
If no other person enters the race by May 1, Horgan will be acclaimed NDP leader.
Farnworth told a news conference that the turn of events wasn't what he had planned when he started the contest.
But as he stood beside Horgan and 27 other NDP caucus members, he said, "I sure like the company I'm with. It begins our campaign to elect a B.C. NDP government in 2017 with John Horgan."
Farnworth, the long-time Port Coquitlam MLA, said he and Horgan share a vision to unite the NDP and win the 2017 election.
The New Democrats were touted to win last May's B.C. election, entering the race as 20-point favourites, but voters rejected their platform and re-elected the Liberals under Clark for a fourth consecutive term.
Farnworth said he contacted the Horgan leadership camp after he decided last weekend to leave the race.
"My head tells me it's the right decision. My gut tells me it's the right decision, and in my entire career in politics when the two are in sync, I know it's the right thing to do."
Farnworth, who had yet to pay the $25,000 non-refundable deposit to enter the race, said he had raised the cash, but decided the NDP needs to unite behind a single candidate rather than engage in a leadership contest.
But it appeared Farnworth's campaign wasn't generating the same lift off as Horgan's. He had secured only two caucus endorsements, Saanich MLA Lana Popham and northwest MLA Doug Donaldson, with Golden-area New Democrat Norm Macdonald indicating support for Farnworth.
The majority of the NDP's 34-member caucus had already lined up behind Horgan, even New Democrats in Farnworth's suburban Vancouver area were supporting Horgan.
Farnworth was also singled out for criticism from former NDP premier Mike Harcourt, who announced recently he didn't renew his party membership. Harcourt said he publicly endorsed Farnworth for party leader in 2011, but hadn't spoken to Farnworth for three years.
Harcourt said the party had made a series of blunders and needed a strong leader to regain his support.
Horgan told a news conference New Democrats work best when they're united.
"Mike Farnworth, thank you so much. I couldn't be prouder of him today," he said.
The NDP leadership convention to replace Adrian Dix was set for September.
Dix resigned last year, months after the May election defeat.
Horgan is considered a traditional populist New Democrat who possesses a quick wit to counter Liberal attacks and has a practical approach to economic development issues, giving him the potential to bridge the divide between resource development supporters and environmentalists.
Liberal energy critic Bill Bennett said he and Horgan have spared for years on energy issues, but now that Horgan is poised to be party leader, he will have to take firmer stands on controversial issues like the proposed Site C hydroelectric dam project and natural gas development in Northern B.C.
Bennett also suggested Horgan will have to do more to keep his emotions in check if he becomes party leader.
Horgan has had to apologize in the past for comments he's made in the legislature.
"The public is fine with genuine," said Bennett. "The public is good with sincere. The public is good with mistakes as long as you apologize when you make one. The public is not good with callousness or meanness or sheer anger. I think he's going to have to really watch out for that in the future."
Dix said he didn't have any problem with Horgan being acclaimed leader. Former NDP premiers Harcourt and Dave Barrett were both acclaimed party leaders, said Dix.
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