The endorsement was announced on Tuesday, along with a statement from Koch lauding Thompson’s track record of fighting for new school seats and reclaiming parkland as chairman of Manhattan’s Community Board 6, which stretches along the East Side from East 14th to East 59th streets.
"The coming years will be challenging for New York City, with a new mayor and speaker of the City Council and dozens of new council members taking office," Koch said in a statement.
"With such a major shift, we need to elect people who understand how the city runs and how to get things done. I know that by electing Mark we will be putting the city in good hands, no matter what challenges we face," Koch added.
Thompson, who worked for the three-term mayor when Koch was still in office, said the endorsement gives his campaign a "powerful push" forward.
"Mayor Koch’s leadership during one of the city’s most difficult times is unmatched, and he is an icon and a hero to New Yorkers," Thompson said.
"Having been a part of his team while he was mayor was a significant part of my life, and his leadership inspired me," Thompson added. "We have spent time discussing the challenges that face the district and the city, and I am very proud that he believes I am the right candidate."
Thompson launched his campaign a few weeks ago to fill the District 4 City Council seat soon to be vacated by Dan Garodnick, who is planning to run for city comptroller. The district includes the neighborhoods of Stuyvesant Town/Peter Cooper Village, Murray Hill, Tudor City, Midtown East and the Upper East Side.
Koch has also endorsed City Council Speaker Christine Quinn as his top candidate for the 2013 mayoral race.