Today, after serving nearly 47 years in the Senate, Daniel Inouye (D-Hawaii) becomes the third-longest-serving Senator in U.S. history, passing Sen. Edward Kennedy (D-Mass.), who died in August.

“I’m not celebrating that day because I’m too busy to do that,— Inouye said. “I think it’s an achievement, to think that I’ve lasted that long.—

In addition to this milestone, Inouye, 85, a former House Member, will also be the fifth-longest-serving Member of Congress in history, passing Rep. Carl Vinson (D-Ga.), who served from 1914 to 1965 and chaired the Armed Services Committee.

Inouye, chairman of the Appropriations Committee, and Kennedy were both elected to the Senate in November 1962, although Kennedy got a jump in seniority because he won a special election to fill the remainder of the term won by his brother, President John F. Kennedy.

Only West Virginia Sen. Robert Byrd (D), the longest-serving Senator in history, and Sen. Strom Thurmond (R), who represented South Carolina from 1954 to 1956, when he temporarily resigned, and again from 1956 to 2003, have served longer in the Senate than Inouye.

Inouye is up for re-election in 2010 and is a shoo-in to win a ninth term.

Inouye’s Congressional service dates to Aug. 21, 1959, when he entered the House as Hawaii became the 50th state. He served in the House for three years, then won election in 1962 to succeed retiring Sen. Oren Long (D).

One of the most memorable events of his tenure was serving on the Senate Watergate Committee from 1973 to 1974, Inouye said. He turned down an offer to be on the committee five times because he was worried about what it would mean for his re-election campaign, he said, but eventually then-Majority Leader Michael Mansfield (D-Mont.) all but forced him to join.

Inouye recalled with a chuckle that Mansfield said: “No. 1, whoever serves on the committee has to be a lawyer. That cuts down the number. No. 2 … anyone who has aspired for the presidency is not qualified, and that leaves you.—

Inouye admitted that he was surprised when the committee became a national news sensation. One major benefit of the televised hearings for Inouye was the rise in his popularity. During the hearings, the Senator got a phone call from George Gallup of the Gallup Organization confirming his high profile.

“He says, ‘This may seem unbelievable, but the best-known person in Washington is the president, according to our polls, and next is you,’— Inouye said. “I said, ‘That can’t be!’ And he said, ‘Oh yes, because you’re the only non-Caucasian on the panel, so whether you like it or not, you stand out.’—

To this day, Inouye said, people come up to him and say they weren’t doing their homework in high school and college in order to watch the Watergate hearings.

Although Inouye has spent decades in Congress, he still has a long way to go before he moves up to longest-serving Member ahead of Carl Hayden (D), who represented Arizona in the House from 1912 to 1927 and the Senate from 1927 to 1969. Even so, second-place Byrd is poised to surpass Hayden next month and set the longevity record.

Rep. John Dingell (D), who has represented Michigan for nearly 54 years, is in third place in Congressional service, and Jamie Whitten (D) of Mississippi, who served in the House from 1941 to 1995, is in fourth — though Inouye would pass him if he is re-elected next year and serves through October 2012, when he will be 88.