"The entire verdict is unacceptable," Song said, adding that he was confident his client's innocence would be affirmed by a higher court.
The five-year sentence is one of the longest prison terms given to a South Korean business leader.
Park, who was forced from office in disgrace, is facing her own corruption trial, with a ruling expected later this year.
Hundreds of rowdy, diehard Park supporters rallied outside the court earlier in the day to demand Lee's acquittal.
Samsung, founded in 1938 by Lee's grandfather, is a household name in South Korea and a symbol of the country's dramatic rise from poverty following the 1950-53 Korean War.
But over the years, it has also come to epitomise the cosy ties between politicians and powerful family-controlled business groups - or chaebols - which have been implicated in a series of corruption scandals.