The politician has promised to introduce a wider consultation process before planning permission is given to tall buildings in the capital.
The statement comes after the Friends of Richmond Park charity raised alarm bells over a new 42-storey building in Stratford which has obstructed a historic view of the cathedral.
Under current regulation, development in the background of St Paul's should be "subordinate to the cathedral and that the clear sky background profile of the upper part of the dome remains".
The new building, Manhattan Loft Gardens in Stratford, is more than 3km away and therefore not restricted by current planning laws. Because of this, there was no public consultation on protecting the view.
Speaking to the Times, Khan said he could extend the area in which consultations on the impact on views of St Paul's should be held.
"Consideration is to be given to including more distant boroughs to prevent this happening again," he said.
"However, this would currently need government agreement unless the necessary powers are delegated to the mayor, as has been sought."
Friends of Richmond Park welcomed the proposal.
A spokesman told the paper: "We would like the mayor to assure us that there are no other tall buildings in Stratford or elsewhere that are in the protected view line and have been granted permission already or are likely to be before the protection is extended."