Daniel Mann pleaded guilty to two counts of fourth-degree animal cruelty on Wednesday.
Mann told the judge he was suffering from insomnia and dealing with family issues when he said he "snapped."
Under a plea agreement, the 31-year-old Belmar resident will face jail time, restitution and community service when he's sentenced in November.
Authorities say workers at the Monmouth County SPCA shelter in Eatontown saw Mann slam a cat headfirst onto the floor in March. A second cat was later found strangled.
The cats were up for adoption.