Aboh (41), who represented the Khonsa West constituency, was seeking a re-election from the seat.
Initial reports suggested that seven people were killed in the attack, but Director General of Police (DGP) S B K Singh put the death toll at 11 later in the day.
Aboh was on his way to his constituency from Assam, along with family members, three police personnel and a poll agent, when the suspected NSCN rebels opened fire at their vehicles near 12 Mile area in the district at around 11.30 am, Singh told PTI.
One security officer, who sustained injuries in the incident, has been admitted to a hospital in Dibrugarh, Assam, the DGP said, adding that the MLA and ten others were killed on the spot.
Expressing his shock over the incident, Chief Minister Pema Khandu said the perpetrators will be hunted down.
"Action will be initiated to hunt down the perpetrators. My heartfelt condolences. May the departed souls rest in peace," he said.
Condemning the attack, NPP president and Meghalaya Chief Minister Conrad K Sangma sought the intervention of the Prime Minister's Office and Union Home Minister Rajnath Singh.
"The NPP is extremely shocked and saddened by the news of the death of its MLA Shri Tirong Aboh (Arunachal Pradesh) and his family. We condemn the brutal attack and urge @rajnathsingh and @PMOIndia to take action against those responsible for such attack," Sangma tweeted.
Meanwhile, the Arunachal Pradesh Congress Committee blamed the ruling Bharatiya Janata Party for the "prevailing lawlessness and chaos" in the state.
"If elected representatives of the state are not safe under the present dispensations at the Centre and the state, how can common people feel secure," the party said in a statement.
Demanding a high-level judicial inquiry into the incident, it also said, "Chief Minister Pema Khandu and his BJP government are solely responsible for lawlessness and all chaos in the state."
Aboh was elected from the Khonsa West seat in 2014 on a Peoples' Party of Arunachal (PPA) ticket. Assembly polls were held concurrently with Lok Sabha elections in Arunachal Pradesh.