John Healey was speaking after a one-day visit to Kyiv on Friday, where he discussed plans for the Multinational Force Ukraine with President Volodymyr Zelensky.
The money will pay for upgrades to vehicles and communications systems, counter-drone protection and other equipment to ensure troops are ready to deploy.
Mr Healey said: “We are surging investment into our preparations following the Prime Minister’s announcement this week, ensuring that Britain’s armed forces are ready to deploy, and lead, the Multinational Force Ukraine, because a secure Ukraine means a secure UK.”
After the meeting Mr Zelensky said he was “grateful” for the UK’s support, adding: “It is crucial that the framework for ending the war includes a clear response from the allies should Russian aggression be repeated.”
Mr Healey’s visit to Kyiv comes days after Sir Keir Starmer pledged to send troops to Ukraine as part of a “reassurance force” organised by the “coalition of the willing”.
The size of the western force, which will also include soldiers from France, has not yet been announced, nor has the Government provided details of how many British personnel it expects to deploy.
Reports have suggested the whole force could amount to just 15,000 men, with the UK providing half the total.
But in the Commons on Wednesday, Mr Healey declined to give details, saying it would “only make (Vladimir) Putin wiser”.
On Friday, Mr Healey also announced that production would start this month on new Octopus drones for Ukraine, designed to intercept other drones used by Russia to attack civilian targets.
The UK aims to produce thousands of the drones per month, with each Octopus costing just 10% of the drones they are designed to intercept.
The announcement comes a day after Russia launched a huge wave of drones and missiles against Ukraine, striking civilian targets and energy infrastructure.
The attack involved more than 200 drones and 20 missiles, according to a British Defence Intelligence assessment, including an experimental hypersonic Oreshnik missile launched against Lviv, in western Ukraine.
The Oreshnik, an intermediate-range ballistic missile (IRBM), is believed to have been fired from 1,000 miles away and well within Russian territory.
Production of IRBMs was banned by the 1987 Intermediate Nuclear Forces Treaty between the US and Russia, but the treaty collapsed in 2019 amid repeated accusations of Russian non-compliance.
Defence Intelligence said Moscow was likely to have only a “handful” of Oreshnik missiles, which cost far more than other missiles it has used to attack Ukraine, adding its use was “almost certainly intended as strategic messaging”.
