The event gives Modi, a nationalist facing international criticism over a recent crackdown in disputed Kashmir, a chance to energise his relationship with Indian-Americans who are active political supporters. Trump, meanwhile, will face a largely foreign-born audience that may not prove receptive to his typical strident anti-immigrant messages.
Jubilant supporters dressed in everything from ornate saris to simple dhotis and even a few cowboy hats waved American and Indian flags, chanted "Modi! Modi!" and munched on concession stand snacks that included Indian staples of samosas and naan breads - along with nachos.
"Trump is very welcome here today. This event is to build harmony and love," he said, standing just in front of the dais where Trump and Modi would speak. "Race, religion and political parties don't matter today."
Houston is a rare Democratic stronghold in Republican-dominated Texas and serves as the economic anchor of a state that will be critical to Trump's 2020 re-election bid. Polls show tepid support by Indian-American voters, some 75% of whom voted for his Democratic rival, Hillary Clinton, in 2016.
But organisers of the "Howdy, Modi!" event that was kicked off with a 90-minute cultural program featuring 400 costumed dancers, say Trump can expect a receptive audience.
It will not be the first time Modi, who heads the Hindu nationalist Bharatiya Janata Party, has addressed a large crowd in the United States, which is home to about 4 million Indian-Americans including about 300,000 in Houston and nearby Dallas, according to a Pew Research Center analysis of US Census data.
Some 19,000 people turned out for a similar event in New York in 2014, and Indian-American volunteers living in US suburbs helped run a telephone blitz of voters in India in the run-up to his May re-election campaign.
KASHMIR CRACKDOWN
Modi's visit to Houston comes ahead of this week's UN General Assembly in New York and amid a particularly tense time on the subcontinent.
The Indian leader further strained long-simmering relations with Pakistan last month by revoking the partial autonomy enjoyed by Muslim-majority Kashmir, which both nuclear-armed countries claim. Modi's move has been met by international criticism.
Members of India's religious minority Sikh and Muslim groups are planning noisy gatherings near the stadium to protest Modi's Kashmir policy.
The US-India relationship on trade and tariffs is rocky, though Trump and Modi appear to have strong personal ties.
But Devesh Kapur, director of Asia Programs at Johns Hopkins University, who has written a book on Indian-Americans, said that while the rally has symbolic value for both leaders, "it's unlikely by itself to impact thorny trade issues ... but it can't hurt."
Kapur also forecast little improvement regarding Trump's standing with Indian-Americans.
"The Trump administration's hard-line policies on immigration ... have hardly endeared (him) to the community," Kapur said. "Appearing with PM Modi might mildly help but certainly not reverse the community's overall pro-Democrat leanings."