He is a substitute for the Committee on Legal Affairs, a member of the Delegation to the EU-Chile Joint Parliamentary Committee and a substitute for the Delegation for relations with the countries of Central America.
Grandes entered politics in 1977 when he was elected as a UCD deputy for Guadalajara in the Spanish General Election. He was re-elected in 1979 but lost his seat at the 1982 election. When the UCD disbanded in February 1983, he joined the Democratic Popular Party (PDP) and returned to Congress at the 1986 election. The PDP merged with other parties in 1989 to form the current PP, for whom he was re-elected at the 1989, 1993, 1996, 2000 and 2004 General Elections.