"Dion brings to our club a great deal of experience and leadership," Rob Blake, the Kings' vice president and general manager, said in announcing the deal. "He also plays with a physical edge, which complements our lineup well."
The Senators are retaining 25 percent of Phaneuf's $7 million salary-cap hit, so the Kings get a top-four defenseman for $5.25 million over the next three-plus years.
The trade will end up saving the Senators nearly $4 million, as Gaborik makes less money in base salary than Phaneuf through the duration of their contracts through 2021.
Phaneuf, 32, is in his 13th season and has three goals and 16 points this season. He is a three-time All-Star, with his last appearance coming in 2011-12 with Toronto.
"The business is the business, and it's a business decision that the Ottawa Senators wanted to move me," Phaneuf said on Tuesday night.
He was pulled from Tuesday night's game against the Penguins in the second period, an indication that something was about to happen with him on the trade front. Phaneuf said he wasn't immediately told about the trade, but suspected something was afoot.
"To be honest with you, I want to thank the Ottawa Senators organization for my time with them, first and foremost, I have nothing but great things to say about the city of Ottawa, about the organization, about my time here," he said. "It's disappointing when you do get moved. But with saying that, I am very excited about where I am going, to the team I am going to, and about being a Los Angeles King. I am honored to be going there, I am excited about the team they have, where they are in the standings. I am going to go there and do the best I can to help their team."
Phaneuf indicated that the move to California would be beneficial for him and his wife, actress Elisha Cuthbert.
"For me, personally, with her there, it's a good situation," he said.
Ottawa coach Guy Boucher said he has seen a player pulled from a game before, but that it made an odd night even odder for the Senators.
"I've seen it before. It's a weird night. Having to pull out Dion made it weirder," said Boucher, who said he didn't address Phaneuf's sudden absence with his team.
"I didn't get into it. Everybody knew what was happening, there was no need to address it. It's a business, it's a tough part of the business," Boucher said. "We're talking about two players that I really enjoyed having around, because they were two character people that brought a lot of positive things to us. Two players that I really respect. Two guys I have been far in the playoffs with. You develop relationships with players. I've always said: Players, not numbers. They are tremendous individuals that deserve the best."
Gaborik, 35, is another veteran whose best years are behind him, with the last of his three All-Star selections coming in 2011-12. He has 403 career goals, but just seven this season in 29 games. He earns $4.875 million per year through 2020-21.
Thompson, 33, has just 52 goals in 593 career games. Shore, 26, has a 4-11-15 line in his fourth NHL season.
ESPN's Greg Wyshynski contributed to this report.