Police in Warsaw cordoned off Pilsudski Square for several hours on Saturday after reports that a man had threatened to blow himself up.
Police spokesman Sylwester Marczak said officers had seen the man climbing onto the Smolensk monument at about 10am local time.
Local media said he had threatened to blow himself up.
He surrendered to police around three and a half hours later.
Private broadcaster Polsat News shared footage that showed him climbing down from the monument, taking off his jacket and walking away with his hands in the air.
"They approached him but then there was a very worrying statement which indicated that there was a very real danger for people on the square," Mr Marczak said, adding that police were now examining his backpack using an x-ray to make sure it was safe.
Pictures posted on social media platform X, formerly Twitter, showed a man standing on top of the monument, which commemorates the victims of an air disaster in 2010 that killed 96 people including Polish president Lech Kaczynski and his wife, Maria.
The man can be seen wearing a backpack and holding something in his hand.
“At the moment negotiations are going on, on the scene there are negotiators and counter-terrorist officers,” a police representative told Reuters earlier on Saturday, urging members of the public to stay away from the area.
“No entrance, there is a bomb,” a police officer on the scene told a Reuters reporter.
Poland is holding parliamentary elections on Sunday.
The country's de facto leader is Lech Kaczynski's surviving twin, Jaroslaw Kaczynski, while his ruling Law and Justice party is fighting for an unprecedented third term in a row.