Foreign Secretary William Hague says the UK's commitment of an extra £5m in non-lethal equipment to the Free Syrian Army is "the right thing to do".
The extra practical support for the opposition FSA will include more radio and satellite equipment, as well as portable power generators.
However, the assistance will not include any weapons.
The BBC's James Robbins says the move is a significant shift in policy after frustration about Syria's opposition.
Aside from concerns about divisions within the opposition, there have also been complaints that it has failed to set out a clear programme for good government, our correspondent added.
Attempts to oust President Bashar al-Assad have led to 17 months of unrest, during which activists claim more than 20,000 people have died.
However, reports of casualties often cannot be independently verified.
Supplies fundingThe UK is also telling opposition forces they must observe human rights standards.
Speaking at a press conference, Mr Hague said the £5m was "in addition to, and separate from, our humanitarian assistance".
Syrian people need "urgent help" and "cannot wait indefinitely" for a peaceful resolution to the conflict, he added, describing them as being at the "mercy of a regime that is hunting down its opponents".
"This is assistance that will help save lives, not abandon all Syrians to the mercy of the regime.
"It will help people caught up in a terrible conflict. It will be delivered in co-ordination with other countries. It is the right thing to do, while not pausing for a second in our efforts to secure the united robust diplomatic action which this crisis demands."
He said the money will be used for medical supplies such as trauma kits, surgical equipment, medicines and water purification. It will also be used to assist local Syrian doctors with the means to gather forensic evidence for any potential trials in future.
The funds will also be spent on communications equipment to help political activists, such as mobile phones, satellite phones and radar equipment.
The foreign secretary added that body armour would be provided for civilians who were involved in the protection of others.
Mr Hague, who also described the Assad regime as "doomed", said it remains British policy not to send arms to Syria.
Humanitarian aid
The Foreign Office says it will help protect activists from repression and help them overcome the Syrian government's jamming and blocking techniques.
It said Britain has previously made £1.4m available in "non-lethal support to the political opposition". This has included providing training and assistance to human rights groups in Syria.
Funding totalling £27.5m is also being provided by Britain for humanitarian aid such as food, medical care and shelter in Syria, as well as for Syrian refugees who have fled to neighbouring countries. Some 800 of these also need assistance with water sanitation.
International Development Secretary Andrew Mitchell had announced this week that the amount of assistance being given to the refugees was being quadrupled.
This support follows on from the £18.4m in humanitarian assistance given by Britain to Libya during the uprising against Colonel Gaddafi last year. This included supplying shelter for both refugees and those made homeless, supporting mine clearance and also helping the World Health Organization to provide medical care.
