The "topping out" ceremony marked work to repair the stonework of the north transept of Leicester Cathedral.
From the roof, The Very Reverend David Monteith offered prayers for the cathedral and city.
Leicester Cathedral was awarded Â£130,000 to "undertake urgent repair work" by the World War One Centenary Repairs Fund last year.
The cathedral team said it was traditional for stone masons to have a topping out ceremony and decided it would be in the form of a blessing service.
Dean Monteith said: "As the city launches its pre-Christmas events and activities, it is very appropriate that we are able to offer our own blessing with the sign of the cross from the roof of a cathedral which has stood for faith at the heart of our city and county for the past 1,000 years".
The cross has been placed on the highest parapet on the north transept of the Guildhall Lane cathedral. New mounting has replaced a weather-worn version put there as part of the mid-19th century rebuilding of St Martins.
Source: Leicester Cathedral architect, Ian Salisbury
As well as the stone cross, a new flame finial has been made to sit on top of a smaller pinnacle, and a new griffin constructed to replace a decayed one.
Repairs have also been carried out to a large window in the north transept and the replacement of gutters and downspouts has taken place across the whole building.
The work is due to be fully completed before the end of the year.
The Dean of Leicester has climbed scaffolding on a cathedral spire to bless a new stone cross.