Anyim was elected into the
Nigerian Senate in May 1999, and was subsequently voted by colleagues as President of the Senate in August 2000, after
Chuba Okadigbo had been impeached, holding office until May 2003.{{cite web |url=http://allafrica.com/stories/201001110722.html |title=What Will David Mark Be Remembered For? |work=Vanguard |author=Emmanuel Aziken |date=9 January 2010 In May 2001, Anyim declared that the upper legislative house was justified in probing the activities of the Mines and Power Ministry during the tenure of Chief
Bola Ige.{{cite web |url=http://allafrica.com/stories/200105290123.html |title= Ige Must Be Probed - Anyim |work=P.M. News |author=Babajide Kolade-Otitoju |date=29 May 2001 In June 2002, an attempt led by Anyim to impeach President
Olusegun Obasanjo collapsed.{{cite web |url=http://allafrica.com/stories/200206250166.html |title=Anyim: Truly Ambushed |work=ThisDay |author=Amanze Obi |date=25 June 2002 Speaking a year later, Anyim said President Olusegun Obasanjo misunderstood him on certain issues but there was no conflict between them.{{cite web |url=http://allafrica.com/stories/200306091039.html |title=Obasanjo Misunderstood Me - Anyim |work=Vanguard |author=Tony Edike |date=9 June 2003 In August 2002, he said he was opposed to all the present office holders - including himself - going for a second term.{{cite web |url=http://allafrica.com/stories/200208190448.html |title=Pius Anyim's Hypocrisy |work=ThisDay |author=Tunji Bello |date=19 August 2002 In November 2002, Anyim indefinitely suspended Senator
Arthur Nzeribe of
Imo State due to an allegation of a N22 million fraud. Nzeribe was said to be planning an impeachment motion against Anyim.{{cite web |url=http://allafrica.com/stories/200211200559.html |title=Anyim Vs Nzeribe, Another Rumble in the Jungle |work=Vanguard |author=Olorunnimbe Farukanmi |date=20 November 2002 The same month, after Anyim had complained about the
Independent Corruption Practices and Other Related Offences Commission (ICPC), the Senate set up a committee to examine the continued relevance of the commission.{{cite web |url=http://allafrica.com/stories/200211200141.html |title=Senate Moves to Scrap Anti-Graft Panel |work=ThisDay |author=Bature Umar And Kola Ologbondiyan |date=20 November 2002 In May 2003, Anyim warned an Abuja High Court judge, Justice Egbo Egbo, that the parliament had the power to order his arrest over his opposition to the passage of the anti-graft ICPC law by the Senate.{{cite web |url=http://allafrica.com/stories/200305120099.html |title=ICPC Act: Anyim Threatens Judge's Arrest |work=Daily Trust |author=Shakirat Abdulmajeed |date=12 May 2003 ==Later career==