Donal Drohan, who lived in Harrow, west London, was killed when a tree fell on his car in Watford this morning.
The ferocious weather also claimed the life of a 17-year-old girl who died after a tree fell onto a mobile home in Kent.
Meanwhile, two people died in a suspected gas explosion caused by a falling tree in Hounslow, west London.
A 14-year-old boy was swept out to sea in what the coastguard described as "atrocious" conditions and the coastguard has called off the search.
British Prime Minister David Cameron has said the loss of life as a result of St Jude's storm is "hugely regrettable".
The deaths came as commuters across the southern part of Britain faced disruption on road, rail and air transport services after the storm battered the UK bringing with it winds of almost 100mph.
The weather system, dubbed the St Jude's day storm after the patron saint of lost causes and 'cases despaired of', whose feast day is today, has brought down trees across the region and according to overnight reports has damaged property and left many roads impassable through floodwater.
The storm hit the South West late last night before tracking north eastwards across England and southern Wales throughout the morning.
More than 270,000 homes in total have been reportedly left without electricity.
Meanwhile, Aer Lingus said it had been forced to cancel a number between Dublin and London Heathrow as well as one flight each way between London Heathrow and Cork and Belfast as southern England and Wales brace for a major storm overnight, which is expected to bring hurricane-force winds and heavy rain.
Ryanair spokesman Robin Kiely said the airline was reviewing the situation, while a number of ferry crossings between Ireland and Britain have been cancelled. All intending passengers are asked to look at the various travel companies’ websites for updates.
In Britain, one tree devastated three houses when it fell on a gas main and led to an explosion in Hounslow, west London. An elderly woman was taken to hospital following the explosion and three people were rescued by London Fire Brigade.
A double-decker bus has also reportedly "rolled over" in Suffolk, injuring the driver and several passengers.
Around 130 flights have been cancelled at Heathrow airport. Network Rail has said there will be disruption on all train services in and out of London and many train companies have cancelled all of their services before 9am.
Developments at a glance
* Donal Drohan, originally from Waterford, was killed when a tree fell on to his car in Watford, north London.
* Two killed in suspected gas explosion caused by failling tree in Hounslow, west London.
* 17-year-old girl killed after a tree fell onto mobile home where she was sleeping in Kent
* Whitehall was closed both ways between Parliament Square and Horse Guards Avenue due to a collapsed crane.
* Storm force 11 winds were reported at Dover.
* A gust of 99mph (159km/h) was recorded on the Isle of Wight.
* Boy feared dead after being swept out to sea in New Haven, East Sussex.
* An empty passenger train has hit a tree near Ivybridge station in Devon.
* Severn crossings between South Wales and England have reopened.
* Network rail reporting more than 100 railway line blockages.
* Sussex Police tweeted that there were 125 trees down across roads in the county by 6.30am.
* UK Power Networks says up to 270,000 households are without power across England.
* Heathrow Airport said around 130 flights had been cancelled.
* Transport for London (TfL) said there was disruption to six Underground lines due to debris from the storm on the tracks.
* Both reactors in Dungeness power station's B units have been automatically shut down
* Royal Botanic Gardens at Kew in south-west London was closed today because of damage caused by the weather.
Many rail services that had hoped to be running reduced services before lunch are still badly affected - with some advising against travel for the rest of the day.
Parts of the country remain on flood alert with the Environment issuing 12 flood warnings for the South West, as well as 131 flood alerts for the rest of England and Wales.
The public had been warned to expect the possibility of power cuts, trees blocking roads and transport disruption.
A boat is dragged from its mooring on the beach and destroyed by large waves near Brighton Marina, in southern England A boat is dragged from its mooring on the beach and destroyed by large waves near Brighton Marina, in southern England Anticipating disruption, the Metropolitan Police urged people to avoid calling 999 during the storm unless there is a real emergency.
A spokesman said: “Calling 999 when it is not an emergency can reduce our effectiveness at dealing with genuine emergencies.”
In Newquay 100 properties were left without power for part of the night, and emergency services were called out to almost 40 incidents.
Sharon Taylor, assistant chief constable for Devon and Cornwall Police, told the BBC: "So far we have had 122 weather-related incidents, that includes 19 reported areas with localised flooding.
"We have put out over 100 extra police officers, including over 50 special constables. I am pleased to say that the majority of incidents are those reported by our own staff and other agencies out on the road, so it does seem that the public have taken to heart the advice we have been giving out over the weekend.
"We have got a significant number of flood warnings in place and certainly at least 19 areas where we have got localised flooding at the moment.".
She added that police were considering evacuating up to 30 properties at Axminster because of flooding, rather than wind damage.
Ms Taylor said volunteers in 4x4 vehicles were poised to get out around the two counties to help with flood and wind damage.
A police car was damaged by a falling tree on the B2104 in Sussex, officers said, while a car also hit a fallen tree in Langney Rise, Eastbourne. The driver was uninjured, police said.
However, Met Eireann forecaster Jim O'Brien said most of the country was expected to emerge fairly unscathed from the Atlantic storm, which is expected to pass over the south of Ireland early this morning as it moves towards the Welsh coast.
"The storm is approaching but it's expected to pass to the south overnight," he told the Irish Independent.
"We should avoid it unless something terrible happens," he added.
Today will remain blustery as more seasonal weather accompanied the official start of Winter Time yesterday.