Julián Castro, the federal housing secretary under Barack Obama, announced his presidential bid on Saturday with an address in his home city of San Antonio, Texas, where he served for five years as mayor.

Delivering remarks in both English and Spanish, Castro said: “When my grandmother got here almost a hundred years ago, I’m sure she never could have imagined that just two generations later, one of her grandsons would be serving as a member of the United States Congress and the other would be standing with you here today to say these words: I am a candidate for president of the United States of America.”

The 44-year-old, who rose to national prominence with an electrifying keynote speech at the 2012 Democratic convention, becomes the second high-profile Democrat to announce their candidacy for 2020, following Massachusetts senator Elizabeth Warren’s campaign launch at the end of last year.

Castro, whose grandmother came to the US from Mexico in the 1920s, will vie to become the party’s first Hispanic-American nominee amid a field of that could swell to more than 20 candidates. The Hawaii congresswoman Tulsi Gabbard also declared a bid on Friday.

The father of two, who trained as a lawyer before entering politics, made a suite of campaign promises during his maiden speech. He vowed to introduce universal pre-kindergarten for American children by expanding a program he introduced as mayor of San Antonio. He also promised to bring the US back into the Paris climate change agreement with his first executive order and pledged comprehensive immigration and criminal justice reform. He named a number of unarmed black men and women killed by police in recent years, in impassioned support of the Black Lives Matter movement.

Castro spent little time criticizing the Republican currently in the White House, but with reference to his recent visit to the border in south Texas, where he decried a “crisis”, Castro said: “Well, there is a crisis today – it’s a crisis of leadership. Donald Trump has failed to uphold the values of our great nation.”

Suppporters in San Antonio as Juliàn Castro announces his candidacy. Photograph: Suzanne Cordeiro/AFP/Getty Images

Castro also pointed to the press risers and, in a marked contrast to Trump who frequently criticizes journalists at his rallies, thanked reporters for their work.

“I know that the press work hard and that they are the friend of the truth in this country,” he said.

Perhaps most pivotally, in the infancy of this Democratic primary, Castro came out in support of universal healthcare with reference to his own grandmother’s treatment for diabetes during her old age.

“Thank God there was Medicare there for her,” he said. “Medicare should be there for everybody. It’s time for Medicare for all, universal healthcare for every single American.”

The policy is likely to divide the field of prospective Democratic candidates, with moderates favouring less expansive reform. The candidate has also backed the progressive wing of the party by signaling support for higher tax rates on the super wealthy.

Castro’s twin brother, the Texas congressman Joaquin Castro, spoke before his brother, acknowledging to the crowd of around 3,000 people who basked in the morning sun that his brother faced stiff competition.

“I’ll be honest there will be a lot of great candidates in this campaign,” he said. “A lot of them are friends of ours.” He described his brother as“the best candidate with the best ideas and the best heart”.

Castro was introduced to the stage at the Plaza Guadalupe amphitheater in west San Antonio by his mother, Rosie Castro, a famed civil rights activist from this city of 1.7m in south central Texas.

“It is time to make sure that opportunity is made possible for every individual in this country,” she said. “I want to introduce to you a son of San Antonio. A son of Texas. And a son of the West side. A son of this country.”

Julian Castro in 2014, when he was housing secretary under Barack Obama. Photograph: Andrew Harrer/POOL/EPA

Since his time in Obama’s cabinet, Castro has slipped away from the limelight as a new crop of young Democrats, including the California senator Kamala Harris and the former Texan congressman Beto O’Rourke, have gained notoriety. Harris and O’Rourke are also seriously considering presidential runs.

Castro was vetted as a potential vice-presidential running mate to Hillary Clinton in 2016, but was overlooked as the Virginia senator Tim Kaine was given the role.

Campaign volunteers said a few hundred people had been turned away at the gates of the event on Saturday, which drew a diverse crowd. A mariachi band and local artists entertained the throngs before Castro appeared on stage.

Brandy Sanchez, 40, had brought her four-year-old son and 16-year-old daughter to watch “history being made”.

“It was so important for them to see this,” Sanchez said. “No matter what happens now he’s made his mark in history.”

Within minutes of the campaign launch the Republican National Committee launched an online attack meme, attempting to discredit Castro’s time in federal and local office.

The candidate will travel to events next week in Puerto Rico and New Hampshire.