In 1962, he was appointed Dean of Law at the University of Saskatchewan, the youngest person to be appointed to that position, and served until 1969.
Lang was elected to the Canadian House of Commons in the 1968 election, and was re-elected in the 1972 and 1974 elections as the Member of Parliament for Saskatoon—Humboldt. He served as Minister without Portfolio (1968-70), Minister responsible for the Canadian Wheat Board (1969-79), Minister of Manpower and Immigration (1970-72), Minister of Justice and Attorney General (1972-75), Minister of Transport (1975-79), Acting Minister of Communications (1975), Acting Minister of Justice and Attorney General (1978), and Minister of Justice and Attorney General (1978). He was defeated in the 1979 federal election by Bob Ogle of the New Democratic Party.
Following his career in politics, Lang served as the Executive Vice-President of Pioneer Grain Co. Ltd., Chairman of the Transport Institute at the University of Manitoba and as President, CEO of Centra Gas Manitoba Inc. He is currently retired, but serves as a director of several companies, including Investor's Group and the Winnipeg Airport Authority. In 2005-06 Lang served as the co-chair of the Federal Liberal Election campaign for Manitoba.
A Rhodes Scholar, Lang holds a BA and an LL.B from the University of Saskatchewan, a B.C.L from Oxford University (Exeter College) and an LL.D from the University of Manitoba. He played for the Oxford University Ice Hockey Club, winning two Blues.
In 1999, he was made an Officer of the Order of Canada.
Lang is married to Madame Justice Deborah McCawley of the Court of Queen's Bench. They currently reside in Manitoba. Lang is the father to seven children (one deceased, Maria), including Andrew Lang, the federal Liberal candidate for the riding of Toronto-Danforth, Timothy Lang, a Vice-President at OneConnect, Gregory Lang, Chief Operating Officer for Solera Sustainable Energies Company, Elisabeth Lang, Legal Counsel for Industry Canada, Adrian Lang, a lawyer and partner with the law firm of Stikeman Elliott and Amanda Lang, a television personality on Report on Business Television. He is also the father of two step children: Andrew Parkinson, a political aide, and Rebecca Parkinson, a university student in Winnipeg.
Federal Riding of Saskatoon East
|- |OGLE, Bob ||align=right|15,234 |- |MEYERS, Dan ||align=right|13,256 |- |LANG, Otto ||align=right|12,631 |- |HOLTORF, Gary ||align=right|117 |- |NEUFELD, Eric ||align=right|64 |}
Federal Riding of Saskatoon Humboldt
|- |LANG, Otto |align="right"|23,243 |- |FRIESEN, Julius |align="right"| 11,826 |- |RHEAUME, Gene |align="right"|11,592 |- |HOLTORF, Garry |align="right"| 548 |}
|- |LANG, Otto |align="right"|24,733 |- |TAYLOR, George |align="right"| 16,426 |- |BRAND, Lewis |align="right"| 12,533 |- |BLACK, Gerald G. |align="right"| 463 |- |REID, James |align="right"| 102 |- |ZAMULINSKI, Brian |align="right"| 89 |}
|- |LANG, Otto |align="right"| 15,210 |- |TAYLOR, George |align="right"| 14,655 |- |BRAND, Lewis |align="right"| 14,444 |}