Gov. Gavin Newsom of California released four years of federal tax returns this week, a disclosure aides said was driven in part by a federal investigation into the finances of his wife, Jennifer Siebel Newsom.

In 2024, the most recent year released, the couple reported a taxable income of about $1.39 million, which included more than $1 million from investments. Mr. Newsom had taxable wages of about $192,000 from his salary as governor, and his wife’s wages were about $148,000.

It was the first time Mr. Newsom, a Democrat, and his wife had released returns since he ran for re-election in 2022. When he was first elected governor, he had promised to release his tax returns annually but did not do so.

Mr. Newsom’s office said it was releasing the documents now to counter right-wing claims that the Newsoms had enriched themselves during his time as governor.

The returns, which were released for 2021 through 2024, show that Mr. Newsom’s finances have been fairly stable over the years, except in 2021, when the family’s income received a $1 million boost after they sold a multimillion-dollar home. Mr. Newsom has filed for an extension to file his 2025 return, which is due in October.

Tax returns often do not indicate how much a person’s wealth has grown through investments and business holdings. Many asset classes grew substantially in value between 2021 and 2024, yet the Newsoms’ income remained roughly the same. The governor and his wife both have significant investments in blind trusts, and only the income from those investments was reflected in the tax returns.

In 2022, the governor posted his tax returns to a state website in compliance with a state disclosure law. This time, his office required journalists to examine 718 pages of tax documents in person on Thursday and take notes with pen and paper.

The financial disclosures show that Mr. Newsom and Ms. Siebel Newsom continued to earn the bulk of their income from Mr. Newsom’s investments in the wine and hospitality industry, which have been held in a blind trust since he became governor. The overall picture from the tax returns tracks the annual financial disclosures that Mr. Newsom was required to publicly file each year.

The disclosures come as Mr. Newsom, who was elected governor in 2018 and is serving his last year in office, weighs a run for the presidency in 2028.

Mr. Newsom and other California Democrats have criticized President Trump for withholding his tax returns ever since he first ran for the White House in 2016. Presidential candidates are not required to release their tax filings but had done so for decades after the Watergate scandal.

Mr. Newsom signed a bill in 2019 that would have required presidential candidates to release five years’ worth of tax returns to appear on the ballot in California, but the law was struck down by the state supreme court. Candidates for governor in the state must still provide their tax forms.

In June, Mr. Newsom said the Justice Department was investigating him and his wife and described it as a politically motivated probe on the part of the Trump administration. While the scope of the investigation is unclear, Mr. Newsom’s aides have said that it is focused in part on his wife and that agents had interviewed people connected to her nonprofit groups.

The governor’s office said in a statement to reporters reviewing the tax documents that “the returns reflect consistent financials over the four-year period” and that they “contradicted the false right-wing claims that the Newsoms ‘enriched themselves’ through new ventures and nonprofit organizations.”

According to the tax returns, two nonprofits associated with Ms. Siebel Newsom accounted for a modest share of the family’s income. For instance, in 2024 Ms. Siebel Newsom earned about $150,000 in wages from the Representation Project, an organization she started in 2011 that uses film and media campaigns to address gender stereotypes.

The disclosures also show that another of her ventures, a production company called Girls Club Entertainment that produces films that explore social issues, has consistently lost money in recent years, while Ms. Siebel Newsom has been paid little. For example, in 2022 the company lost $37,393, and her tax return shows she was paid $11,700.

The couple has paid an effective federal tax rate of 30 percent to 35 percent over the four years. In total, they paid $2.79 million in federal taxes and about $500,000 in California state income tax.

The couple also paid additional taxes for domestic staff members and babysitters. The couple reported paying nearly $200,000 in wages for household employees in 2024.

Mr. Newsom, who this year published a memoir, “Young Man in a Hurry,” earned $70,000 as an author in 2023 and an additional $75,000 in 2024. It was unclear if that money was an advance for the memoir or was related to a children’s book he published in 2021 about a boy with dyslexia, a condition Mr. Newsom has managed his entire life.

The Newsoms’ taxable income of $1.39 million in 2024 was 18 percent lower than in 2019. But the couple had a lucrative year in 2021, reporting taxable income of $3.5 million, reflecting a gain of more than $1 million from the sale of a home in Marin County. Their investment income also jumped that year.

Over the four years, the couple’s charitable donations ranged from a low of $40,000 in 2021 to a high of $67,000 in 2023. The names of the organizations they donated to in cash were withheld, but the recipients of their noncash donations were listed. For example, in 2022 they donated “Armani business wear” to a restorative justice organization in Oakland. On the form, the couple said the clothing had cost them $45,000, but they estimated its “thrift shop value” at $4,900.

Other donations include furniture, toys, books, appliances and household goods to Goodwill Industries Sacramento Valley and Northern Nevada.