"We will contest in all the 45 seats. We will go it alone. We will win," GJM General Secretary Roshan Giri told reporters after the party's core committee meeting here.
He said that the names of the candidates would be announced soon.
GJM president Bimal Gurung has not yet decided on whether he will contest or not, party sources said.
Gurung together with a GJM delegation had met West Bengal Chief Minister Mamata Banerjee at the state secretariat in Kolkata on June 28, where he had said he would announce the decision about his party's participation in the polls after the core committee meeting.
One of the priorities of the Trinamool Congress chief was the restoration of peace in Darjeeling after her party came to power in the state.
On July 18 last year, a tripartite agreement was signed between the GJM, and the West Bengal and central governments for setting up the GTA, which would replace the Darjeeling Gorkha Hill Council (DGHC) formed in the late 1980s.
Among its salients points were that the central and state governments and the GJM, keeping on record the GJM's demand for a separate state of Gorkhaland, agreed to form an autonomous body -- the Gorkhaland Territorial Administration -- through direct elections.
The autonomous self-governing body would administer the region so that the socio-economic infrastructural, educational, cultural and linguistic development was expedited and the ethnic ideas of the Gorkhas established.
The GTA Bill was passed in the state assembly on September 2 last year.
Altogether nine parties, including the Congress, have so far decided to contest the polls.
The Gorkha National Liberation Front (GNLF) had earlier decided not to participate.
