The BDP had boycotted parliament altogether, holding its own sessions in the Kurds' unofficial capital, Diyarbakir.
On Friday, two bombs exploded at an election rally in Diyarbakir, killing three and wounding hundreds of others.
By contrast, thousands of jubilant Kurds flooded the streets of the south-eastern city of Diyarbakir as the results came in.
After Friday's deadly attacks in the southeastern city of Diyarbakir, he urged supporters not to take to the streets and tweeted: "Peace will win".
After completing his studies at the prestigious Ankara University, Demirtas worked as a human-rights lawyer in Diyarbakir before going into politics in 2007.
After bombs killed two people and wounded more than 200 at an HDP rally in Diyarbakir, in the mainly Kurdish south-east, on Friday, Selahattin Demirtas, the HDP leader, condemned Erdoğan's silence.
The election breakthrough for the leftist HDP, a new party largely representing the Kurds but also encompassing liberals nationally, was greeted with wild celebrations in the Kurdish-majority city of Diyarbakir in south-eastern Turkey.
In the most serious attack so far, two bombs exploded in the main Kurdish city of Diyarbakir, killing at least two.
Enough of Erdoğan and his anger," said Seyran Demir, a 47-year-old who was among the thousands who gathered in the streets around the HDP's provincial headquarters in Diyarbakir.
The Dogan agency is quoting unidentified military sources as saying that at least 25 additional F-16 fighter jets were deployed at Turkey's Diyarbakir air base late Monday.
He became aware of his Kurdish identity at the age of 15 after he attended a funeral of a prominent politician who is believed to have been murdered by security forces in Diyarbakir, Turkey's main Kurdish-majority city.
