But business records show Ms Babbage was appointed to the role in 1998.
Pecuniary interest register declarations are supposed to be made within a month.
The revelations come after News Corp Australia revealed earlier this year Arthur Sinodinos, tipped to be Mr Hockey's right-hand man as finance minister in an Abbott government, failed to declare six company directorships in his first year in the upper house.
Mr Hockey yesterday suggested he was clueless about his wife's business interests for 14 years and would not explain what the company did.
He insisted that his register was now fine and that he was the victim of a Labor Party smear campaign.
"As I become aware of my wife's commercial interests I declare them, as is appropriate," Mr Hockey said.
"My pecuniary interest register is entirely in order."
A spokesman for Special Minister of State Mark Dreyfus said: "The long-standing practice of parliamentarians' declarations of interests is an important element of our transparent democratic process."
Australian Securities and Investments Commission show Mrs Babbage was appointed as a director of Steel Harbour Pty Ltd on April 2, 1998.
Her directorship includes the three years Mr Hockey was a member of the Howard ministry from 2004 to 2007 and spans more than some of the long careers of Mr Hockey's colleagues.
Mr Hockey was elected as the member for North Sydney in 1996.
But Mr Hockey's register of pecuniary interests shows he only put the interest on the public record on May 29 last year.
Mr Hockey said: "The Labor Party has previously engaged in this type of muckraking and then been forced to correct such unsubstantiated assertions. It is a desperate action from a desperate government."
MPs can be referred to a privileges committee inquiry over omissions with the interests register.
Punishments for knowingly providing incorrect information to parliament can include jail or fines.