IF POLITICS IS a game of addition, put Sen. Will Brownsberger down in the plus column.

The lead sponsor of a sweeping criminal justice reform bill convened a marathon rally on behalf of the legislation at the State House that started on Thursday morning and ended in the afternoon. No fewer than 29 speakers took to the microphone in front of the marbled Grand Staircase to make the case for a bill that supporters hope will translate into the biggest changes in the state criminal justice system in decades.

The roster included 13 state senators, 15 advocates of various stripes, and the district attorney from the state’s most populous county.

Senate President Stan Rosenberg addresses Thursday’s rally for criminal justice legislation.

“We need to lift people up instead of locking them up,” Brownsberger said kicking off the gathering that stretched on for nearly two hours. “And we need to cut the chains that hold people down when they’re trying to get back on their feet. That’s what this bill is about, from front to back.”

Brownsberger, the Senate chairman of the Joint Committee on the Judiciary, said the state is incarcerating four to times as many people as it did 40 years ago.

The bill he has crafted would touch on nearly every area of the criminal justice system. It would repeal some mandatory minimum sentences for lower-level drug dealers; set new regulations in place for the use of solitary confinement in prisons; eliminate some of the fines and fees that advocates say can hold back offenders when they’re released from incarceration; and reform the state bail system. The bill would also raise the age for most cases handled in the adult criminal justice system to 19 and decriminalize consensual sex involving minors who are close in age.

“We need to sweep out the cobwebs from the system so that we get better outcomes,” said Senate President Stan Rosenberg. He said there’s something wrong when conservative southern states are “trendsetters” in reforming their criminal justice systems and Massachusetts is playing catch-up.

Brownsberger, a Belmont Democrat, said after the rally that its goal was to “just keep building awareness of bill and the motivations behind it and the support for it. “

Asked about the lengthy line-up of speakers, he said it was also important to acknowledge the range of groups and the number of fellow senators who are committed to seeing significant reform enacted this year. “They need to see each other and recognize how many different people are coming together behind this, and hopefully we all take from it strength to continue to apply ourselves to the difficult task before us,” he said.

Jefferson Alvarez of the Lowell-based organization UTEC speaks at the rally.

That big-tent approach meant including speakers who said they were supporting the bill even though it doesn’t address everything they would like to see changed.

“We know that the glass is not completely full,” said Beverly Williams of the Greater Boston Interfaith Organization. “But it is half full.”

Middlesex District Attorney Marian Ryan applauded the bill’s expansion of the use of “restorative justice” approaches to resolve cases in ways that bring offenders and victims together. “We have not fallen for kneejerk reactions that are born of fear or revenge,” she said of the months of discussions that preceded drafting of the bill.

In a statement issued last week, Ryan said she supported many elements of legislation, including the repeal of some mandatory minimum drug sentences, while also having “concerns about some parts of the bill.”

Representatives from three groups — the ACLU of Massachusetts, Prisoners’ Legal Services, and the Committee for Public Counsel Services – attended the rally but did not speak because of reservations they have about the legislation. Their concerns include criticism that it does not go far enough in repealing mandatory minimum sentences and establishes new mandatory sentences for some drug trafficking offenses. They also expressed concerns that some of the bail reform provisions could make it easier, not harder, to hold people on high bail before trial.

Brownsberger said there is still work being done on the bill, and some of the concerns may be addressed when the bill is released by the Senate Ways and Means Committee next week.

Sen. Sonia Chang-Diaz, a Jamaica Plain Democrat, said it’s crucial to “stop being patient” and maintain pressure to pass a major bill this session. “Many times we have been told, next year, next session, after this election we’ll deal with the problems of racial disparities in sentencing, failed war on drug tactics, and the fiscal and human drain of mass incarceration,” she said.  “This bill that the Senate is going to take up this month is the bill that we need today.”

“Keep up the noise,” Sen. Sonia Chang-Diaz tells supporters of the bill.

She also urged a focus on the possible, not the perfect. “It does not include all of the things that I have advocated for, but it is comprehensive in breadth. It recognizes that our system is broken in so many places, and it tackles that from the front end to the back end.”

She thanked advocates for their “righteous impatience” and encouraged them to “please keep up the noise in the weeks to come.”

With nearly half of the Senate showing up at the rally – 18 senators made appearances – the bill’s prospects in the 40-member body seem clear. The “noise” is more likely to be directed at the House, which leans more to the right and where Speaker Robert DeLeo has been guarded in his comments about what he’d like to see in a bill.

Leaders of the 57-member House Progressive Caucus released a letter late Thursday to Rep. Claire Cronin, the House chair of the Joint Committee on the Judiciary, listing five priorities for reform legislation in the House. The list includes repeal of mandatory minimum sentences for drug crimes; bail reform and expansion of restorative justice and diversion programs; and creating a system to allow expungement of juvenile criminal records.