Former crime series actor Fred Thompson ended his presidential bid Tuesday, dropping out of the Republican nomination race after his campaign as a "true conservative" failed to catch fire.

Thompson, 65, bowed out after finishing a distant third in Saturday's Republican primary in South Carolina behind Senator John McCain and former Arkansas governor Mike Huckabee, winning just 16 per cent of the vote.

"Today I have withdrawn my candidacy for president of the United States," Thompson said on his website. "I hope that my country and my party have benefited from our having made this effort."

A gravel-voiced Southerner, Thompson launched his candidacy in September 2007 and placed himself right of centre with positions such as a limited role for the federal government.

Some supporters compared the former lawyer and ex-senator from Tennessee to Ronald Reagan, the Hollywood actor who became US president and a conservative icon in the 1980s. But Thompson never generated the money or momentum to match, while US media described his campaign as lacklustre.

He failed to win any of the six state preference polls held so far by the Republican Party to choose its candidate for the November 4 presidential election. As a Southern state like his home state of Tennessee, South Carolina had been viewed as a make-or-break contest for Thompson.

Thompson played a prosecutor on the long-running crime series Law and Order and also appeared in the big-screen Cold War thriller The Hunt for Red October.

He served in the US Senate for more than eight years until 2003 and, as a young lawyer was on the Republican staff of congressional investigations into the Watergate scandal in the early 1970s.