Miriam Gonzalez Durantez said she was "willing to help" the Liberal Democrats but being an international lawyer and mother-of-three took up most of her time.
Gordon Brown and David Cameron have both indicated that their spouses will be employed to win votes as they bid to present a more personal image to the electorate.
The Lib Dem leader and "first lady" were seen on television last night talking about their relationship and home life following similar interviews involving the other spouses.
They spoke to ITV's Mary Nightingale about falling in love and choosing names but Mrs Gonzalez Durantez said she would not push forward any "sugar-coated image" of herself.
Objecting to the description of her as a "political wife", she insisted: "I'm the wife of a politician. I don't have a role, I'm just married to him."
Asked if she would join the campaign trail along with Sarah Brown and Samantha Cameron, she said: "I am willing of course to help Nick, because he is my husband.
"I want the best for him and of course I love him. I'm willing to help the party, and I'm willing to help the party because I'm willing to help what I defend. There is a core set of principles that I just cannot wait to see them implemented in the country.
"How am I going to do that while I have children and I have a busy job? Well, listen, I don't have the luxury of having a job that I can simply abandon for five weeks, and I imagine that that is the situation for most people in the country.
"Whatever I can fit between the job and the children I will do it 150 per cent."
What the other wives did was a "personal choice", she said.