The South American country will be the first in the world to legally sell the drug over the counter for recreational use.
The move was set in motion in 2013 with a law that fully legalised the cannabis trade.
However, it has been a slow process to put the law into practice.
"Cannabis will be dispensed in pharmacies starting in the month of July," presidential aide Juan Andres Roballo told a press conference.
The law requires buyers to sign up to a national registry, which Mr Roballo said would be up and running by 2 May. The price will be US$1.30 (Â£1) per gram.
Registrants - who must be Uruguayan citizens or permanent residents - can purchase up to a maximum of 40 grams (1.4 ounces) per month.
The marijuana sold will come from state-supervised fields.
The law also allows users to grow their own at home, or join  cooperative clubs that farm it.
Many pharmacists have doubted the financial benefits of selling a cost-controlled product.
Some Uruguayan buyers were also reluctant to sign up to a national registry, complaining of the invasion of their privacy and of having to keep to the monthly limits.
The government has now done a deal with 16 pharmacies, but it hopes to sign up more.
Mr Roballo said there would be a public health campaign before the registry was opened.
He also said the government was not close to covering the predicted demand, but it does not believe there will be "an avalanche of users" signing up,

Shares in Barclays fell 0.9% after the US Department of Justice sued the bank for alleged mortgage securities fraud.
It says Barclays misled investors about the quality of loans backing securities in the run-up to the financial crisis. Barclays has rejected the claims
Data showed the UK economy grew faster than estimated in the third quarter.
The Office for National Statistics (ONS) said the economy grew by 0.6% in the July-to-September quarter, compared with the previous estimate of 0.5%.
However, the ONS also trimmed its growth estimates for the first and second quarters of the year.
On the currency markets, the pound fell 0.2% against the dollar to $1.2258, and slid 0.4% against the euro to â‚¬1.1725.

The woman, believed to be Lithuanian, was struck by a car on the A38 near Burton-upon-Trent around 20:30 BST on 6 July after leaving the man's vehicle.
Johnathon Allison, of Colman Street, Hull, has also been arrested on suspicion of murder.
Mr Allison was remanded in custody at Cannock Magistrates' Court on 8 July.
See more stories from Stoke and Staffordshire here
Staffordshire Police said Mr Allison has been released under investigation in connection with the murder probe.
He will next appear at Stafford Crown Court on 11 August.
Police said the woman left the vehicle as it pulled into a layby, and was hit at "high speed" by an oncoming car.
She was airlifted to hospital in cardiac arrest with head, chest and pelvic injuries, but later died.
Police are now working with authorities in Lithuania to confirm the identity of the woman.
Uruguay will begin selling cannabis in pharmacies from July, the final stage in the country's pioneering regularisation of the drug.
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UK shares edged higher in the final trading session before Christmas, with the FTSE 100 ending a shortened session up 4.49 points at 7,068.17.
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A man has appeared in court charged with breaching a restraining order following the death of a woman on a dual carriageway.