Scouted by singer Lee Sun Hee, Lee Seung Gi was trained for 2 years before debuting on June 5, 2004 at the age of 17. Because You're My Girl, his debut song from his first album The Dream Of A Moth, was a very popular ballad and created a "liking older women" syndrome in South Korea. With this song, he won the "Best Newcomer" award in various music awards ceremonies in 2004 (such as M.net KM Music Festival, SBS Music Awards and MBC Best 10 Singers Music Festival). In 2007, he also won the "Best Male Solo Artist" award[1] in the M.net KM Music Festival with his song White Lie from his third album Story Of Separation. He released a digital single Will You Marry Me in 2009, which became a big hit in South Korea although there was no official promotion. With this single, he received the "Digital Single Bonsang" award[2] in the 24th Golden Disk Awards.

In 2005, Lee Seung Gi guest-starred in MBC's sitcom Nonstop 5. He then officially debuted as an actor in KBS's 2006 weekend drama The Infamous Chil Sisters. In 2008, he was offered the main character role in MBC's historical drama The Return of Iljimae, but was forced to turn down the offer due to his tight schedule. He was cast as the main male character of SBS's weekend drama Brilliant Legacy in 2009, starring with Korean actresses Han Hyo Joo and Moon Chae Won. The drama maintained its top spot in viewer ratings for ten consecutive weeks and ended on July 26, 2009 with its 28th episode attaining a high viewer rating of 47.1%[3]. The huge success boosted Lee Seung Gi's popularity as an actor in both South Korea and overseas. With this drama, he received the "Best Actor (Special Production)" award, the "Top 10 Stars" award and the "Best Couple" award with Han Hyo Joo in the 2009 SBS Drama Awards[4].

Lee Seung Gi is currently a permanent member of 1 Night 2 Days, a segment of KBS's Sunday variety show Happy Sunday. He debuted in the 15th episode on November 11, 2007. In 2008, he received the "Best Popularity" award[5] in the KBS Entertainment Awards for his high popularity in 1 Night 2 Days. Lee Seung Gi took up another MC role in SBS's variety talk show Strong Heart[6] in 2009, co-hosting with Kang Ho Dong, who is also the main MC of 1 Night 2 Days. Although it was a relatively new variety show on SBS, Strong Heart was recognised as the "Best Program"[7] at the 2009 SBS Entertainment Awards and Lee Seung Gi was also awarded the "Netizens' Popularity" award[8] after receiving the most number of votes in the online poll.

Despite his busy schedule, Lee Seung Gi was able to graduate from Dongguk University within 4 years, obtaining his degree in International Trade and Commerce on February 20, 2009 and receiving a Special Achievement Award[9] from the university. He is currently continuing his studies in the Graduate School of Dongguk University.