"I believe Texas needs a strong, independent voice to address the enormous challenges we are facing -- leadership that focuses on results rather than politics," Sanchez, a Democrat and former Army lieutenant general, said in a statement released by his campaign.
Sanchez, who now lives in San Antonio, said he'll make a formal public announcement in the coming weeks.
The Democratic Senate Campaign Committee has identified Texas as one of the six Republican-held seats the party hopes to pick up in 2012. Democrats hold a slim 53-47 majority in the chamber, and must defend 23 of their seats next fall.
Democrats see changing demographics as reason for optimism in Texas, a state where for decades the party hasn't had much success. New census data showed that the Latino population grew 42% in Texas from 2000 through 2010, and now accounts for more than a third of the overall population.
Party strategists also think Sanchez's military experience will be an asset in the state, but he can expect to face questions about his leadership of U.S. forces in Iraq from 2003 to 2004. Some of the same lawmakers he would caucus with if elected were among the most critical of his tenure, particularly in connection with the Abu Ghraib prisoner-abuse scandal.
An Army inspector general's report largely cleared him of wrongdoing, but he later wrote in his memoir that he was denied a fourth star in part because "Senate Democrats were intentionally putting pressure" on the George W. Bush administration "not to send my nomination forward."
Republicans have a crowded primary in the race to succeed GOP Sen. Kay Bailey Hutchison, who is retiring. However, the party is bullish no matter who its nominee is, saying the Democratic candidate will have to answer for President Obama's policies that are unpopular in Texas.
"We’ll leave it to national Democrats to crow about their latest handpicked candidate, because as any observer of Texas politics knows, we’ve heard it all before and we have no doubt this seat will remain in Republican hands," said National Republican Senatorial Committee spokesman Brian Walsh.