The Model Code of Conduct immediately comes into force from Saturday in both the states.
The Election Commission also announced by-elections for one Lok Sabha seat in Bihar and 64 assembly constituencies spread across 18 states.
Single-phase assembly elections will be held in Maharashtra and Haryana on October 21 and the Bharatiya Janata Party will take on the Congress-led opposition to retain power in both the states.
The date for the polls in the two states was announced by the Election Commission on Saturday.
The counting of votes will be taken up on October 24, Chief Election Commissioner Sunil Arora told a press conference.
The term of the 288-member Maharashtra assembly ends on November 9 and that of the 90-member Haryana assembly on November 2.
Notifications for the two assembly elections will be issued on September 27 and the nomination process will begin on the same day. October 4 is the last date of filing nominations.
While scrutiny of nomination papers will take place on October 5, October 7 is the last date for candidates to withdraw from the electoral battle.
The Model Code of Conduct immediately comes into force from Saturday in both the states.
The assembly elections are the first after Prime Minister Narendra Modi led the BJP to power at the Centre for a second term in May.
The government's decision to abrogate Article 370 provisions, which gave special status to Jammu and Kashmir, is among the BJP campaign's key themes for the assembly polls.
BJP leaders sound confident of retaining power in both the states, where opposition parties have been weakened with many key leaders from their camp joining the saffron party in the recent weeks.
In Maharashtra, the alliance between the BJP and the Shiv Sena has not been finalised yet, though talks between the two parties have been going in for some time.
The BJP wants to fight a larger share of the 288 seats in the assembly while the Sena wants it to stick to the earlier agreed formula that both will contest an equal number of constituencies.
Both parties could not agree to a seat-sharing deal even in the 2014 polls, leading to them fighting the elections separately.
The BJP had won 122 seats and the Sena 63 seats.They joined hands after the polls to form government.
Asked why elections to the Jharkhand assembly were not announced on Saturday when the country was discussing simultaneous polls, Arora said the term of the state assembly there ends on January 9.
"If the leader of the House there wants to dissolve the assembly and advance the elections, then it is a separate matter. But why should the commission want to advance it," he said.
While there is a debate on simultaneous polls, "unless there is a very clear consensus amongst the political parties on the issue, this cannot be taken as a given template", the chief election commissioner said
Arora was also asked whether the EC will ban the use of Article 370 in election campaigns as it had banned the use of actions taken by defence forces across the border. He did not spell out a clear reply.
"(Article) 370 is a decision taken by the Parliament of India. The only place where it can be challenged is the honourable Supreme Court of India," he said.
Referring to the use of paper trail machines, he said on the lines of the Lok Sabha polls, the commission has mandated that VVPAT slips count of five randomly selected polling stations in each assembly constituency of
Haryana and Maharashtra will be done for verification of the result obtained from the electronic voting machines.
The commission also reiterated that while some EVMs fail to function due to "mechanical, structural or physical defect" including faulty switches, broken button, faulty connection, these never record a "wrong vote".
The polling stations where the count is taken up are selected by a draw of lots after the election and before counting.
The EC will set up 95,473 polling stations for over 8.95 crore voters in Maharashtra. In Haryana, 19,425 polling stations will be set up for nearly 1.83 crore voters.
Bypolls to 64 assembly seats and one Lok Sabha constituency spread across 18 states will also be held on October 21 and the counting of votes will be on October 24, the Election Commission announced.
While assembly by-elections will be held on 64 assembly seats, the Samastipur Lok Sabha constituency in Bihar will also have a bypoll.
These assembly seats include 15 in Karnataka and 11 in Uttar Pradesh.
Arora said the byolls in Karnataka will be held on seats, including where sitting MLAs were disqualified recently.
The 11 UP assembly seats mostly belong to MLAs who had won the Lok Sabha elections and had resigned as members of the state assembly.
The Samastipur (Bihar) Lok Sabha by-election was necessitated following the death of sitting MP Ram Chandra Paswan of the Lok Janshakti Party in July.
Responding to a question, Arora said the bypoll to the Satara Lok Sabha seat will not be held along with the Maharashtra assembly elections on October 21.
Satara MP from Nationalist Congress Party Udayanraje Bhosale had recently joined the Bharatiya Janata Party after resigning from the Lok Sabha.
Assembly bypolls in West Bengal are not being held now as the state government had cited the Durga Puja festivities to postpone the exercise. They will also not be held in Uttarakhand now as panchayat elections are already underway and the state machinery is occupied with the exercise, Arora said.
In some other seats, by-elections are not being held as respective high courts are hearing election petitions and the matters are sub judice, he added.
States where assembly bypolls will be held are Arunachal Pradesh, Chhattisgarh, Telangana, Madhya Pradesh, Meghalaya, Odisha and Puducherry (one seat each).
The other states are Assam (4), Bihar (5), Gujarat (4), Himachal Pradesh (2), Kerala (5), Punjab (4), Rajasthan and Tamil Nadu (two each) and Sikkim (3).
The notification for on the Lok Sabha bypoll and 64 assembly by-elections will be issued on September 23.
The nomination process will begin the same day.
