Garcia's endorsement is seen as a sign that perhaps more progressive members of the Democratic Party may support Kennedy.
In 2016 Garcia was a key national supporter for Bernie Sanders' presidential campaign, and even in Illinois the primary race with Hillary Clinton tightened with Sanders in the final days of the campaign.
Also on Thursday, Kennedy is holding a major fundraiser with the guest of honor, his mother Ethel Kennedy. Several of his sisters also will be in Chicago for the event, which is focused on women supporting Kennedy.
Democrat JB Pritzker has secured the majority of early endorsements. Just this week, Comptroller Susana Mendoza announced her support for Pritzker, joining Secretary of State Jesse White as key state leaders endorsing Pritzker.