"In the next two years, you can be assured that I will pursue my duties, and my responsibilities to our state and people, with the same vigor that I have employed during my Senate service," Hutchison said in an open letter to her constituents posted on her Facebook page.
The 67-year-old senator said she was announcing her decision now to "give the people of Texas ample time to consider who my successor will be."
Hutchison, who lost the Republican gubernatorial primary to incumbent Rick Perry, said she intended to leave the Senate "long before now" but was persuaded to remain to avoid a "disadvantage to our state."
"Instead of putting my seat into a special election, I felt it was my duty to use my experience to fight the massive spending that has increased our national debt, the government takeover of the our healthcare system, and the growth of the federal bureaucracy, which threatens our economy," she said. "I will continue that fight until the end of my term in 2012."
She said she would be "forever grateful" for the privilege of representing Texas in the U.S. Senate and "will now look forward to living full time in Texas with my family, and to keep working for our state's interests as long as I live."