Police Constable Dave Wardell and his German shepherd Finn were attacked in Stevenage in October last year while responding to an earlier report of a robbery.
The teenager from London, who cannot be named because of his age, was found guilty of actual bodily harm against Wardell and criminal damage in relation to Police Dog Finn.
He will be sentenced at a later date, the BBC reported.
Wardell and Finn were attacked in the early hours of October 5 in Denton Road in the Hertfordshire town.
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The officer's hand was stabbed and he was treated in hospital and released.
A teenager from Lewisham, south-east London, was arrested and charged the following day.
He appeared before magistrates at Stevenage Youth Court earlier, and is expected to be sentenced at Crown Court at a later date.
Wardell and Finn have now recovered from their injuries, and returned to work together just before Christmas.
Finn, now aged eight, retired from active duty at the end of March, the report said.