Grondin served as Mayor of Shawinigan-Sud from 1977 to 1985. He did not run for re-election in 1985 and was succeeded by Claude Pinard.
On September 29, 1986, Grondin won a by-election and filled the seat left by Jean Chrétien, becoming the Liberal Member for the district of Saint-Maurice. Chrétien had left federal politics in February that year and would stay out of office until he became Liberal party leader and subsequently Prime Minister.
After serving in the remaining months of the 33rd Canadian Parliament, Grondin left federal politics and did not campaign in the 1988 federal election. He was succeeded by Denis Pronovost of the Progressive Conservative Party.
He died in 2005 after several years of dealing with cancer.