The Democrat's organ donor, New Haven Superior Court Judge Brian Fischer, administered the oath of office to Looney on Wednesday, the opening day of the 2017 session of the Connecticut General Assembly.
"We were close for 30 years. We're going to be close for, hopefully, the next few decades, too," said Fischer.
"What that means for someone who is perfectly healthy himself and yet subjects himself to major surgery to benefit someone else, that's an extraordinary gift and an extraordinary act of generosity," said Looney.
Looney has served in the legislature since 1981. He joked how he now has a "freshman kidney" for the new session.
Looney was elected President Pro Tempore by his colleagues in the Senate, which has an even number of Democrats and Republicans for the first time since 1893.
North Haven Sen. Len Fasano will be the Republican Senate President Pro Tempore. Looney and Fasano worked out a power-sharing agreement shortly after Looney's surgery.