A gloomy morning did not dampen the celebration of Massachusetts’ new transgender accommodations law Monday, as more than 100 advocates joined top state legislators at the steps of the State House.

Attorney General Maura Healey kicked off the ceremony, flanked by Boston Mayor Martin J. Walsh, Senate President Stanley Rosenberg, and House Speaker Robert DeLeo.

“This day is yours, and this bill is yours,’’ said state Senator Sonia Chang-Diaz, a Democrat from Boston and a lead proponent of the bill, beaming.

Republican Governor Charlie Baker, who signed the bill into law Friday, did not attend. Aides said he was meeting with the Mexican consul general at the time.

The new law will allow people to use restrooms, changing rooms, and locker rooms that match their gender identities. It will also protect transgender individuals from discrimination in public spaces such as museums, restaurants, malls, and libraries.

The law will go into effect Oct. 1, though one aspect — the prohibition of advertisements of signs that discriminate against transgender people — will be effective immediately.

Several speakers, including legislators and advocates, took to the lectern over the course of the hourlong ceremony to laud the law, which took nearly a decade to pass.

While many decried how long it took the government to approve the law — similar bills had been filed but failed to make their way through the legislative process since at least 2007, and 17 other states have already enacted similar laws — they said they were glad for the opportunity to gather publicly in support of the new law.

“It puts us back on the forefront of equality on a global scale,’’ Walsh said.

Many speakers called the moment historic.

“I believe that these bills where we take a load off people, where we protect a group of people, these are the bills that we will look back on with the greatest pride,’’ said William Brownsberger, Senate chairman of the joint Judiciary Committee.

The state passed a law in 2011 prohibiting gender identity discrimination in housing, employment, public education, and credit, but did not include a provision for public accommodations.

Several speakers shared personal experiences lobbying for the bill’s passage.

Mimi Lemay, 39, of Melrose, recounted the first time she brought her then 5-year-old son Jacob, who is transgender, to the State House. He was playing on Boston Common, chasing squirrels, but Lemay had to bring him into the building so they could speak with legislators.

“I felt bad dragging Jacob away from the squirrels that day,’’ Lemay said to the crowd. “But we had a job to do, I reminded him, a job that couldn’t wait. So the squirrels would have to.’’

At the end of the ceremony, Healey invited attendees to sign an enlarged copy of the bill, and a crowd of transgender people and advocates rushed to the State House steps. Adorned in bright-colored clothing and rainbow pins, many people hugged and cried.

Dianne Monnin, whose son is transgender, said she was “thrilled’’ that legislators held a public ceremony Monday.

“I was so sad that the bill got signed so quickly and kind of privately,’’ said Monnin, 64, who said she had testified in support of the bill. “So when I heard about this I was like, ‘Great, now we can come and celebrate.’ ’’

Kassandra Howard, who is transgender, said though she wishes a similar law had passed a long time ago, she was happy on Monday to celebrate with friends and legislators.

“I am very proud right now to be a Massachusetts resident.’’

Legislators said they hoped the signing of the bill would send a message to other states debating similar measures. In North Carolina, for instance, the governor signed a bill barring communities from allowing transgender people to use public bathrooms that match their gender identities.

The emotional event was punctuated with loud applause throughout, as each speaker paused to thank legislators and advocacy groups from across the state.

Midway through the ceremony, Representative Denise Provost of Somerville looked up briefly and smiled. The sun, she noted, was beginning to shine.

Meg Bernhard can be reached at meg.bernhard@globe.com. Follow her on Twitter @meg_bernhard.