"We not only will fully support but (will) be part and parcel of this long march," said party spokesman Sadiqul Farooq, adding that Sharif would personally participate.
Farooq said his party is not trying to destabilize the government, which is only about seven weeks old, but wants to remind it "to fulfill its commitment" to reinstate the judges.
Still, the decision to join protests by the popular lawyers' movement could further pressure the larger partner in the coalition, the Pakistan People's Party of Asif Ali Zardari. The power struggle also comes as Pakistan faces growing economic problems and the continued threat of Islamic militancy.
Last week, Sharif pulled his ministers from the Cabinet over the judges issue.
Then came the controversial appointment of a governor in Punjab province who is allied with Zardari's party. Officials from Sharif's party, which heads Punjab's government, have said they are concerned that the new governor might interfere with the provincial administration.
Aitzaz Ahsan, a leader of the lawyers' movement, on Sunday urged popular support for the protests as he laid out the expected route.
"We have given the call for the long march, and the energies of all lawyers of Pakistan, masses and civil society shall be spent to make it a successful event," he said.
Zardari party spokesman Farhatullah Babar said Sharif's supporters had a "democratic right" to march along with the lawyers.
"However, we feel that since the issue of reinstatement of judges is already under consideration the protest demonstrations at this point in time are premature," he said.
Musharraf fired dozens of independent-minded judges in November and declared a state of emergency to avoid legal challenges to his presidency.
The moves sparked widespread protests and fueled anger among lawyers - already upset over the president's previous attempt to get rid of the chief justice.
Lawyers' protests helped undermine Musharraf's grip on power last year. Anti-Musharraf parties swept parliamentary elections in February and vowed to restore the judges. But the parties of Sharif and Zardari could not agree on how to do it.
Sharif's party has demanded outright reinstatement. Zardari's party has linked the judges' restoration to a broader judicial reform package. There also are complex legal and political questions to resolve, such as what will happen to the judges Musharraf installed after the purge, and the future role of the deposed chief justice.
Sharif so far has said his party will not move to the opposition and would support Zardari's party on an issue-by-issue basis.
The widening rift, however, could throw a lifeline to the embattled Musharraf, whose presidency and role in the war on terrorism was long backed by the United States.
Zardari has insisted he can persuade Sharif to return to the government fold. But his reluctance to force a showdown with Musharraf has stirred talk that he might align himself with the president if the coalition collapses.
Babar declined Sunday to say whether the judges could be restored before June 10, but admitted his party's popularity may have "received some setback" over the issue.
"But we are confident that when the judges are finally restored according to the PPP plan the party will be able to not only regain the lost ground but also win much more," he said.