During his term, he announced the declaration of martial law on September 23, 1972, just hours before Marcos himself came on the air.

In 2001, he was one of the 11 senators who voted against opening an envelope that had been alleged to contain incriminating evidence against then Philippine President Joseph Estrada, inciting events that led to the EDSA Revolution of 2001.

[2] Tatad ran again for senator under the Koalisyon ng Nagkakaisang Pilipino of actor Fernando Poe Jr. in 2004 but lost.

In 2007, he resigned from the governing board of the United Opposition as a protest against the party's decision to draft Alan Peter Cayetano, Joseph Victor Ejercito and Aquilino Pimentel III as its senatorial candidates due to issues of "dynasty-building",[3] as the three have relatives already serving in the Senate.

During the hearing on the impeachment of Chief Justice Renato Corona on January 19, 2012, Tatad had a verbal confrontation with Senator-Judge Franklin Drilon, accusing him of acting like a part of the prosecution team.