"The path which consists of applying the law and taking all issues before the courts – that is to judicialize political life – leads us to a disaster, to conflict, and this is what we must avoid," José Manuel García Margallo said during an interview with Cadena Ser radio.
"In politics, as in life, you should always avoid confrontation," he added.
The government should "talk a lot" with Catalans about their concerns that their region pays more taxes to the central government than it should or that Catalonia's distinctive language is at risk, he added.
The former minister was speaking a day after some 80,000 people rallied in Barcelona in support of several Catalan politicians who are facing court cases by the Spanish government for taking steps toward secession.
Prime Minister Mariano Rajoy dropped García-Margallo, 72, from his new cabinet which was sworn in earlier this month. He was replaced by Alfonso Dastis, a more discreet technocrat.
The former foreign minister said there are more supporters of independence in the wealthy northeastern region of Catalonia now than four years ago when Rajoy came to power.
"This is everyone's responsibility," he added.
"We must be firm on the key issues -- the unity of Spain, the equality of all Spaniards -- and very flexible on the issues that have produced this rise in separatism."
García-Margallo also said it was "essential" to avoid an independence referendum in Catalonia planned for September 2017 by the region's current president, Carles Puigdemont.
Catalans have nurtured a separate identity for centuries, with their own language and customs.
Their long-standing demands for greater autonomy have been exacerbated by Spain's recent economic downturn, leaving many resenting the amount of taxes they pay to the central government in Madrid to subsidize poorer regions.