Nick Clegg said on Monday he was "shocked and saddened" by Chris Huhne's dramatic guilty plea to perverting the course of justice.
But the Liberal Democrat leader said the former energy secretary had taken the "right decision" to step down from Parliament in light of the admission.
Clegg, who is expected to make a full statement soon, said: "This is obviously an extremely serious matter and it's essential that the legal process is now allowed to run its course."
"I am shocked and saddened by what has happened, but I believe that Chris Huhne has taken the right decision in resigning as an MP."
Huhne narrowly lost out in the Lib Dem leadership race in 2007 and many believed he still had a chance of supplanting an embattled Clegg.
When Huhne was forced to resign as cabinet minister, Clegg was granted a temporary reprieve from the challenge to his leadership.
It was assumed Huhne would fight the charges against him and make a return to front-line politics.
A conviction for perverting the course of justice puts any leadership hopes to rest as well removing a significant threat to Clegg's leadership.