Italy’s parliament has backed the introduction of same-sex civil unions in a long-awaited decision that has been hailed as a civil rights landmark.

Before the approval by MPs on Wednesday, Italy had been the last major western country not to legally recognise same-sex relationships. However, the legislation was criticised for not providing full equality for gay couples, particularly in terms of adoption rights.

Politicians in the chamber of deputies, Italy’s lower house, voted 369-193 in favour of a vote of confidence in the government, making final approval of the disputed civil unions bill automatic. The bill was expected to be voted through later on Wednesday.

The Italian prime minister, Matteo Renzi, called the confidence vote to prevent potential last-minute blocking or delaying amendments by opponents of the legislation, who include rebels in his Democratic party as well as the Catholic right.

Before the vote, Renzi wrote on his Facebook page: “Today is a day of celebration for so many people. We are writing another important page of the Italy we want ... It was no longer acceptable to have any more delays after years of failed attempts.”

The government used the same confidence vote tactic to ensure that the bill was approved by the senate of the republic, the upper house, in February, but only after the original text had been diluted in order to appease opponents threatening to scupper it altogether.

A draft article that would have granted gay couples the right to adopt their partners’ biological children was dropped. While adoption has not been ruled out, family judges will decide on a case-by-case basis.

Amid concern that civil unions would be too similar to marriage, references to a need for faithfulness were removed. Gay couples will be able to take each other’s names and inherit each other’s residual pension rights, but critics say the new rules fall short of the legal protection offered to same-sex couples in other European countries, as well as Canada and the US.

Claudio Rossi Marcelli, a commentator for Internazionale magazine, who lives with his husband and children in Denmark, said: “For Italian homosexuals and all those who support civil rights, it’s a bittersweet victory.”

Gabriele Piazzoni, the national secretary of equality organisation Arcigay, said in a statement: “The glass is half full. The text contains the recognition and protection many gays and lesbians have been waiting for all their lives ... [but] everything this law has failed to guarantee leaves a bitter taste.”

Several previous attempts to legalise civil unions in Italy have foundered, often due to opposition orchestrated by the Catholic church. In 2007, a mass protest caused the centre-left government of Romano Prodi to abandon a much less ambitious civil unions project. The failure of the bill was cited as one of the causes behind the fall of his government in 2008.

The present bill risked difficulties over the adoption clause, with critics insisting it would open the door to surrogacy, which is illegal under Italian law.

The interior minister, Angelino Alfano, was among the most fervent opponents of providing a legal framework for surrogacy, saying in January that the use of paid surrogate mothers should be treated in the same way as a sex crime.

At the same time, Renzi faced pressure to get a bill on to the statute book from the European court of human rights. Judges at the court ruled last year that Italy had breached its commitments under the European convention on human rights by denying gay couples legal unions.

Opinion polls suggest that public opinion in Italy has moved decisively in favour of civil unions in recent years, but that a majority of voters remain opposed to extending equal adoption rights to gay couples.

The decision to use a confidence vote to push the bill through angered the Catholic church, with Nunzio Galantino, the secretary general of the Italian Episcopal Conference, describing it as “a defeat for everyone”.