Brown has has on Saturday held an "introductory" meeting with National Unity Platform (NUP) President Robert Kyagulanyi.
According to the poll results, Mr Museveni 76-year-old won nearly 59% of the vote, with 38-year-old Bobi Wine trailing with about 35%, the Electoral Commission said.
Vice-Singing Robert Kyagulani - his real name - was elected MP in 2017, and the spokesperson for a young Ugandan is extremely poor and urban, which is not recognized in President Museveni's old regime.
Mr Museveni's NRM party said over the weekend it had assembled a legal team to defend his victory. Bobi Wine scooped 39%.
NHL Highlights | Senators vs Oilers John Gibson made 19 saves for the Ducks in his third loss in a row after the Ducks earned a point in his first three games. Cam Talbot had 22 saves in his return to the crease, his previous game on January 22 when he suffered a lower-body injury.
When the security forces surrounded Bobi Wine's home after the announcement of presidential election results, Ambassador Brown attempted to visit him (Bobi Wine), but was turned away.
There have been challenges to the past four elections that Museveni won, all of which were dismissed by the Supreme Court.
Losing candidates have sought unsuccessfully in the past to overturn Museveni's wins in court. One of Africa's longest-serving rulers, Museveni has won every election since 1996, nearly all marred by allegations of irregularities. That no ballot was invalid at polling stations in rural areas of Isingiro and Kazo, yet there were invalid votes at polling stations in urban places including Kampala, " said Bobi Wine."This fraud will not go unchallenged. Electoral registers were tampered with at other locations, he added. Government shut down the internet ahead of voting day.
Civil society activists have criticised the parameters for challenging Ugandan elections, with judges only examining events on voting day and the declaration of results, without also taking into consideration the overall campaign period.
"The electoral jurisprudence narrows an election process to votes, numbers and statistics on declaration day making election petitions very hard", independent election analyst Crispin Kaheru told AFP.