SAN JOSE, Calif.—A Texas money manager who invested more than $1 million in Theranos Inc. when it was still an early-stage healthcare startup took the stand Wednesday in the criminal-fraud trial of founder Elizabeth Holmes to detail the promises she made that helped convince him to back the company.

The testimony of Alan Eisenman underpins one of the wire fraud charges Ms. Holmes faces in a 12-count indictment, and builds on similar stories jurors have heard from other investors at trial.

Assistant...

SAN JOSE, Calif.—A Texas money manager who invested more than $1 million in Theranos Inc. when it was still an early-stage healthcare startup took the stand Wednesday in the criminal-fraud trial of founder Elizabeth Holmes to detail the promises she made that helped convince him to back the company.

The testimony of Alan Eisenman underpins one of the wire fraud charges Ms. Holmes faces in a 12-count indictment, and builds on similar stories jurors have heard from other investors at trial.

Assistant U.S. Attorney Jeffrey Schenk said after jurors left for the day that the government is likely to rest its case next week. They have so far called 24 witnesses over 10 weeks.

Mr. Eisenman recounted how Theranos was the first biotechnology company he had ever invested in, and that he learned about the company through a close friend in Houston who was a financial adviser to Ms. Holmes’s family.

“He told me Elizabeth was brilliant and she was dropping out of school to start a company,” he told the court.

Mr. Eisenman said he began speaking with Ms. Holmes directly about the company as he was deciding whether to invest. He heard that Oracle Corp. co-founder Larry Ellison was an investor and board member, a detail that he said impressed him. He said he was also swayed when told that Theranos had contracts with a handful of large pharmaceutical companies, including Pfizer Inc. “That put an initial stamp of approval on this investment,” he said.

Jurors have heard over weeks of testimony that Theranos’s work with pharmaceutical companies was minimal, and that the company showed investors documents purporting to offer the endorsement of drug firms Pfizer and Schering-Plough Corp. that prosecutors say were doctored.

Echoing other investors, Mr. Eisenman said that Ms. Holmes was his primary source of information when making his investment, and that he had regular contact with her.

Mr. Eisenman said when he first invested around $1.1 million in 2006 on behalf of himself and his three children, he thought Theranos’s finger-prick technology was already far along. A subsequent investment of nearly $100,000 by Mr. Eisenman in 2013 backs one count of the indictment.

He recalled being told that significant revenue was in the company’s future, including a projection of $200 million in revenue in 2008. Mr. Eisenman testified that he was also told in 2009 that Theranos was expecting demand for 1 million of its blood-testing cartridges a month, which would grow to 2 million a month, and that the company could do multiple tests per cartridge for $30 each. “These are numbers that are pretty astounding and create very significant value for this company,” Mr. Eisenman said.

Mr. Eisenman said he was told Theranos would be cash-flow positive by around 2010, which he called “tremendous news.”

Theranos had zero or near-zero revenue through early 2015, and internally forecast its first substantial revenue of about $113 million at the end of 2015, according to financial documents submitted into court record. It forecast about $200 million in revenue for 2016, eight years after Mr. Eisenman expected it, according to the documents, and the company consistently lost money.

By May 2010, Mr. Eisenman said, he sometimes had trouble getting information that he requested from Ms. Holmes. Jurors saw an email in which he requested estimates on the number of cartridges the company was selling, and asked to set a time for a quarterly update that she had been giving him directly.

After a follow-up email asking for a response, Ms. Holmes wrote back saying that she wouldn’t be able to provide the information he wanted. She said the company didn’t have plans to do an IPO anytime soon and suggested Mr. Eisenman take the company’s offer to buy out his investment at five times what he put in.

Mr. Eisenman said he was more proactive than other investors, and he got the impression management didn’t like it. “There was no information coming from the company,” he said. “To me that’s a sign of trouble.”

His contact with Ms. Holmes eventually dropped to zero, he said, and he began reaching out to Theranos board Chairman Donald Lucas in 2012 for more information. After one time reaching out to Mr. Lucas’s office, he got a response back from Ms. Holmes, shown in court, saying, “Alan, we have communicated about this multiple times before yet you choose to continue going down this path.”

Mr. Eisenman said he read the email to mean that his effort to go around Ms. Holmes “was not taken kindly.”

Despite the frustrations, Mr. Eisenman decided to invest again in 2013, because he was given assurances from Ms. Holmes and the company’s No. 2, Ramesh “Sunny” Balwani, that the technology was working and it was a growing market. He was told early investors could buy into this new fundraising round at $15 a share, and that a larger institutional investor raise would be priced at $17 a share.

He recalled a friendly conversation with Mr. Balwani in 2013, which came after prior hostility. In retrospect, he said, he believes the change could have been because, “When you’re raising money sometimes you put on a different face.”

By 2014, the relationship had soured again, as he renewed efforts to keep tabs on the company. Jurors saw an email Mr. Balwani sent Mr. Eisenman in November 2014, ending with, “please stop sending me emails everyday.”

Mr. Eisenman said he never sold his shares before Theranos went out of business in 2018.

—Heather Somerville contributed to this article.

Write to Sara Randazzo at sara.randazzo@wsj.com