François Compaoré, 63, is wanted in Burkina Faso in connection with the deaths of journalist Norbert Zongo and three companions.
Their charred bodies were found in a burnt-out car in the south of the country.
The crusading editor of L'Indépendant newspaper had written hard-hitting articles about the Compaoré regime.
At the time of his murder he was investigating the death of François Compaoré's chauffeur.
Zongo's family have long accused François Compaoré, who was known as the "little president" during his brother's 27-year reign, of having a hand in the killings.
He stands accused of "incitement to murder", according to their lawyer, Bénéwendé Sankara.
"This arrest is purely and simply a response to the arrogance of a man who is defying justice," he told RFI.
Zongo's widow, Géneviève, said she hoped that it would finally allow her to find out the truth about her husband's death.
"Once you know who killed your husband, you are already a little reassured that justice is being done," she commented. "But when you get no answers, things are not as they should be."
Compaoré's lawyer in France, Pierre-Olivier Sur, claims that his client has been declared innocent by an international commission of inquiry and by a Burkinabé investigation.
The case is a "political manoeuvre", he said.
Campaign to find perpetrators
Press freedom campaign Reporters Without Borders tried to open a case relating to the Zongo killing against the then president when he visited Paris in 2000 but the case was dismissed.
The international inquiry identified six "serious suspects" but only one, a former presidential bodyguard, has been charged and the case against him was dismissed in 2006.
In December 2015 three former members of the presidential guard were charged in connection with the case.
Regime overturned by mass protests
Both Compaorés fled to Côte d'Ivoire after the regime was overthrown by huge demonstrations in 2014.
They took Ivorian citizenship, although François Compaoré's wife lives in France, as do three of his children..
He appeared before French magistrates on Monday and was not detained while extradition is decided on, lawyer Sur said.
"We dare to hope that the French authorities will appreciate the significance of this affair and proceed to extradition," Burkinabé public prosecutor Laurent Poda told the AFP news agency.
But opposition parties doubt the Burkina Faso government's commitment to pursuing the case, given that current President Roch Marc Kaboré was Blaise Compaoré's right-hand man before breaking with him and other former allies are still in positions of influence.
The trial of 107 people accused of involvement in a 2015 coup attempt opened in Ouagadougou last week.
Côte d'Ivoire has refused to extradite Blaise Compaoré, who is the subject of an international arrest warrant in relation to the murder of former president Thomas Sankara in 1987.