Islamabad: He was one of five liberal activists to have disappeared in recent weeks.
All have now returned. Mr Haider’s brother said he was well, but did not disclose where the blogger had been.
The men had aired views critical of the military or militancy on social media. No group has admitted holding them. The government has denied accusations that its secret agencies were involved.
When the activists disappeared in early January, hundreds of people held protests across Pakistan to demand the authorities traced them.
Mr Haider, a well-known poet and university professor, was last seen in Islamabad on 6 January, two days after bloggers Waqas Goraya and his cousin Asim Saeed disappeared in Lahore.
Another blogger, Ahmed Raza Naseer, who has polio, disappeared from his shop in Skeikhupura near Lahore on Saturday.
A fifth activist, Samar Abbas, also disappeared a few days later.Supporters of the men accuse the security services of having secretly arrested them.
During their disappearance, the activists were accused of blasphemy on social media.
Blasphemy is a serious allegation in deeply conservative Muslim Pakistan, and it has prompted further concerns for their safety.