Sirleaf survived a challenge from former diplomat Winston Tubman in last month's presidential election, the second since the country emerged from a bloody civil war in 2003.
Tubman boycotted a runoff vote, handing Sirleaf an easy victory this week. Tubman's camp claimed the country's election committee skewed the contest in Sirleaf's favor, though international monitors said the October contest was largely free and fair.
Sirleaf's spokesman this week said peace and reconciliation would be the top priority in Liberia as the country looked to recover from civil war.
Sirleaf was a co-winner of this year's Nobel Peace Prize, though that gave her little clout at home where her reputation was sullied by ties to figures linked to abuses in the country.
"As a Nobel laureate, of course, I have to go the extra mile in promoting peace and reconciliation in our society," she told U.N. Radio after getting more than 90 percent in the runoff vote. "We are going to reach out to everybody and ensure that they have a participation in what we do."
She added that Tubman has a right to challenge the results but felt the overall outcome would stand.
Liberia's National Election Commission reported that 38 percent of the eligible voters cast ballots in this week's election. Johnson secured 90.4 percent of the vote compared with Tubman's 9.4 percent.