BOSTON — Congressman Joe Kennedy III has decided to run for U.S. Senate, creating a wide open contest for his Congressional seat and setting up a showdown in a Senate field that currently includes incumbent Edward Markey and two other Democrats, Shannon Liss-Riordan and Steve Pemberton.

Kennedy has been weighing a Senate run for weeks and multiple media outlets reported late Wednesday that he'll formally announce Saturday in East Boston. Markey's senior campaign advisor John Walsh issued a statement after The Boston Globe reported about Kennedy's intentions.

"In 2013, Ed Markey asked voters to send him to the U.S. Senate to fight for the people of Massachusetts," Walsh said.

"Since then, he has fought on the front lines to show them they were right. Now he wants to continue that leadership on the issues that matter most - climate change, income inequality, gun reform, universal health care, reproductive freedom, and immigrant rights. Elections are about choices, and Ed looks forward to spending the next 14 months campaigning hard every day to show the people of the Commonwealth why he's the right choice. From lowering drug prices for our seniors, to expanding opioid treatment and recovery services, to creating green jobs for our workers, Ed Markey is ready to continue the fight for Massachusetts."

Democratic Treasurer Deborah Goldberg, currently serving in the first year of a four-year term, is considering a run for the seat Kennedy currently holds. Also, according to an advisor familiar with her plans, Alliance for Business Leadership President Jesse Mermell has resigned from that post and plans to launch a Fourth District campaign "within days."