The victory shows that the state government had succeeded in unifying people and the Kerala's politics had "transcended the divisions of caste and religion," Mr Vijayan said soon after the CPM retained the seat with 67,303 votes, nearly 21,000 votes more than the Congress rival.
D Vijaykumar of the Congress, who had led an aggressive campaign to attempt wresting the seat the party has won all but four times, ended up with 46,347 votes, a marginal improvement over his party's performance in the 2016 assembly elections.
The BJP, which had expanded its footprint in the 2016 elections, came third again but couldn't retain the 42,682 votes the party had then scored. This time, PS Sreedharan Pillai, a former Kerala BJP president, came third with 35,270 votes.
CPM leaders say the Mr Pillai's performance in the by-election in Chengannur in Alappuzha district, best known in the country for its calm backwaters, is a reflection of the state's rejection of the BJP's politics.
The by-election was necessitated following the death of sitting MLA KK Ramachandran Nair (CPI-M) in January this year due to illness.
CPI-M state secretary Kodiyeri Balakrishnan said the defeat of the Congress candidate was a rejection of what he called, was the "soft hindutva policy" adopted by the Congress in the constituency as it had done in Karnataka.
Former union minister and Congress leader AK Antony said the party will examine the reasons for the defeat and take corrective steps.
Mr Antony also pointed the dip in the BJP's vote share and said Congress-led United Democratic Front votes had only increased and not declined.
Some of the reduced votes that accrued to the BJP candidate are linked to the BJP's falling out with one of BJP's key ally - the Bharat Dharma Jana Sena (BDJS), a political party that is seen to wield influence with the backward Ezhava community. The BJP apply had kept away from the campaign following differences with BJP.
Get the latest election news, live updates and election schedule for Lok Sabha Elections 2019 on ndtv.com/elections. Like us on Facebook or follow us on Twitter and Instagram for updates from each of the 543 parliamentary seats for the 2019 Indian general elections. Election results will be out on May 23.