However, the 64-year-old former governor of Massachusetts has in effect been running for the last five years, having failed to get the ticket last time around. His main strengths are a good organisational structure and money, lots of it.
Estimated to be in command of a personal wealth exceeding $200m, his team has access to the largest campaign fund - crucial in the primary stage.
And with his movie star looks, charisma and smooth manner, many observers have been led to say that he looks the part.
Born in Detroit, Michigan, on 12 March 1947, Willard Mitt Romney is the son of former Michigan governor and 1968 presidential candidate George Romney, and 1970 US Senate candidate Lenore Romney.
After studying at Stanford University, Romney served in France for 30 months as a missionary for LDS Church.
He married his high school sweetheart Ann in 1969 and the couple have five sons and 16 grandchildren together. In 1998 she was diagnosed with multiple sclerosis and has more recently fought breast cancer.
After his missionary work, Romney attended Brigham Young University and, in 1975, graduated from a joint JD/MBA programme co-ordinated between Harvard Law School and Harvard Business School. He was named a Baker Scholar for graduating in the top 5% of his business school class.
Romney has spent most of his working life in the private sector, rather than in politics, and after working as a business consultant for several years, he founded investment firm Bain Capital in 1984.
His track record led to him being drafted in to head the 2002 Salt Lake City Olympic Games Organising Committee, where he was praised for reducing its budget and restoring public confidence.
From his success there, he went on to become a Republican governor in the Democratic state of Massachusetts from 2003 to 2007, and pledged to use his experience to clean up the "mess" of Washington as president.
Although his success as a businessman means he is seen as the most qualified candidate to jump-start the nation's economy, he is mistrusted by the Republican Party's evangelical wing, due in part to his Mormon faith.