The pair had visited a nightclub in the Sri Lankan capital Saturday during a tour of the country with their team Clems Pirates RFC.
Durham City Rugby Club, which oversees the team, said in a statement the pair suffered "non-rugby related breathing problems".
Mr Baty, also from Durham, who had been critically ill, has also now died.
Mr Howard's death was confirmed in a club statement issued on Monday.
According to the police, British players went to a nightclub after the match and returned to their hotel in the early hours of Sunday.
Thomas Andrew, who played for Durham-based Clems Pirates RFC, collapsed after complaining of breathing difficulties on Sunday night.
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Thomas Baty and Thomas Howard of Durham, England, had been each admitted to hospital in Colombo on Sunday Could 13, complaining of respiratory difficulties.
Mr Howard's post mortem examination did not show any injury or illness and samples have been sent for further analysis, police said.
Police spokesman SP Ruwan Gunasekera reportedly told the Sri Lankan Daily Mirror that the team was staying in a hotel in Colombo after playing their opening match against Ceylonese Rugby and Football Club.
"The club requests that the Howard and Baty families' right to privacy is respected and upheld at this most hard time".
"Both players and Clems Pirates hold a special place in our rugby family, and our continued support is unconditional", said Richard Wilkinson, president of DCRFC.
The British embassy said in a short statement it was assisting the players' families and was in touch with local medical services.