Middlesex County Sheriff Peter J. Koutoujian today launched his bid for the congressional seat set to be vacated by Senator-elect Edward J. Markey.

Koutoujian, a Waltham Democrat and former state representative, announced his candidacy for the Fifth Congressional District in a four-minute YouTube video in which he speaks about his family’s immigrant roots and calls public service his “life’s work.”

Among the issues he mentions in his announcement are the economy, job creation, education and the environment.

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“We need to know that the next representative hears the voices and sees the faces of those that they represent and, most importantly, can get things done to make their lives better,” he says, looking at the camera. “I have dedicated my life to doing exactly that and I’m ready to bring those progressive values and a lot of hard work to Washington.”

Koutoujian, who was appointed sheriff in 2011 and was elected to the position in 2012, joins a crowded Democratic primary field for the seat. State Representative Carl M. Sciortino of Medford, and state Senators Will Brownsberger of Belmont, Katherine Clark of Melrose, and Karen Spilka of Ashland are all running to represent the heavily Democratic district that runs from Revere to Lexington to Framingham to Holliston.

Spilka is set to kick off her candidacy at an event in Framingham tonight.

The date of the special election to fill the seat has yet to be set because Markey has not yet resigned to be sworn in as Senator. That’s expected to happen after the July Fourth holiday weekend.

After that resignation takes effect, state election law calls for Governor Deval Patrick to schedule a special election for a date from 145 to 160 days later, which probably means that the special election will be held in December with an earlier primary contest.