The two were battling for retiring Kay Bailey Hutchison's U.S. Senate seat. Cruz had lost the May 29 primary by a large margin but forced the runoff because Dewhurst fell short of a majority.
Cruz now will face off in November against former Texas state lawmaker Paul Sadler, the winner of the Democratic primary run-off.
Voters on Tuesday also chose a new Republican nominee for Ron Paul's 14th Congressional District in Texas. The Associated Press reported Randy Weber beat opponent Felicia Harris. Now, the Pearland resident will face the Democratic nominee in the general election on Nov. 6.
Paul, who's been a U.S. representative for 16 years, announced he was stepping down before his latest attempt for the presidential bid.
In another race that was the center of a controversy, John Devine has defeated Texas Supreme Court Justice David Medina for the Republican nomination for a spot on the court.
Earlier in the month, Latino leaders in Houston accused of Devine of saying he wanted to run against Medina because he thought he could "beat a guy with a Mexican last name."
Devine denied that claim, saying his wife is Hispanic and his kids speak Spanish and that the allegations were an attempt to "impugn" his character.
Locally, the most race is the Democratic one for Harris County School Trustee Position 6, where former Houston City Councilman Jarvis Johnson is facing off against Erica Lee, daughter of Congresswoman Sheila Jackson Lee.
Earlier this month, the county clerk's office discovered that the wrong district lines were used for the primary in May. It's possible that if the correct lines were used, this run-off would have been unnecessary.
Lee has been leading Johnson in the race since early voting numbers were released Tuesday evening.
But both candidates have different positions on the unique situation their race is in.
"I said whether I win or whether I lose, I was going to stand for the 1,400 voters who did not have a chance to vote. The earlier contention was that in the general election, I won 49.7 percent of the vote. With the 1,400 votes that couldn't be cast, that would have potentially pushed me the 50-percent mark," Johnson said.
"We think teh run-off, as the judge said, can go on, it's going on. There will be a victory declared tonight. All the voters were allowed to vote in this run-off tonight. They've had all the boxes, all the ballots correct so they had the opportunity for the Democratic nominee and they'll have it again on November 6, and that's what we're looking forward to," Lee said.
The Associated Press contributed to this report.