Tobin was born in Stephenville, Newfoundland. He studied political science at Memorial University in St. John's. He worked a brief stint as a TV news announcer before joining the Liberal Party of Canada as a political aide.
Tobin was first elected to the House of Commons as a Liberal in 1980. Though the Liberals were badly defeated in the 1984 federal election, he retained his seat and went on to gain prominence as a member of the so-called opposition "Rat Pack". He supported Jean Chrétien during the latter's second campaign for leadership of the Liberals in 1990.
Following the 1993 federal election in which the Liberals regained power from the Progressive Conservatives after almost a decade in opposition, Tobin was appointed Minister of Fisheries and Oceans for his loyalty to Chrétien.
In the ministry, Tobin distinguished himself from his colleagues with speeches rife with rhetoric and his youthful exuberance. Throughout 1994 he mounted a fierce campaign against foreign over-fishing of waters on the nose and tail of the Grand Banks, located just outside Canada's declared 200 nautical mile (370 km) Exclusive Economic Zone (EEZ). People across Canada took notice of this new and aggressive posture, a position that had not been taken by a federal minister — Liberal or Conservative — since the EEZ was declared in 1977.
Critics note that Tobin was likely doing this to preserve his political life in his home province. At this point, Newfoundland and Labrador was wracked by rapidly rising unemployment and social unrest over the fiscal situation which many believed had been caused by federal mismanagement of foreign and domestic overfishing. This had resulted in the 1990 "Northern Cod Moratorium." In April 1995, Tobin's department was embroiled in the so-called "Turbot War" which pitted Canada against the European Union. Later that month, Tobin conducted an international news conference from a barge on the East River outside the United Nations headquarters and dramatically displayed an illegal trawl net that had been cut from a Spanish trawler which was arrested outside the Canadian EEZ.
Tobin helped organize a pro-Canada rally in Montreal before the October 1995 Quebec referendum — bussing in thousands of university students and other residents from English Canada. For his roles as Fisheries Minister and in the referendum, he earned the nickname "Captain Canada".
In 1996, Tobin resigned from federal politics to pursue the leadership of the Liberal Party of Newfoundland after the resignation of Premier Clyde Wells. Tobin won handily and as Premier of Newfoundland, had the good fortune to preside over the province during an unprecedented economic boom brought on by offshore oil and gas exploration and development, as well as the discovery of one of the world's largest nickel deposits at Voisey's Bay in coastal Labrador. Tobin pursued tough negotiations with out-of-province companies seeking to export the resource for refining and smelting elsewhere, insisting that the resource will never be mined unless Newfoundlanders received secondary manufacturing and tertiary service spin-offs. A similar tough stance was taken in seeking to develop the lower Churchill River, keeping in mind the contract his predecessor Joey Smallwood had been forced to sign. Tobin's Liberals won re-election in 1999.
It was also during this time in the lead-up to the millennium that Newfoundland undertook an aggressive tourism marketing campaign which focused on important anniversaries such as the 500th year since John Cabot's voyage of discovery (1997), as well as the 1000th year since Vikings such as Leif Ericson made landfall on the province's shores (2000). Tobin brought his province international exposure with his negotiations to have Newfoundland's unique time zone and geographic position recognized to a world-wide live television audience as being the first location in North America to celebrate the arrival of the millennium.
In the fall of 2000, Tobin suddenly resigned to join the federal Cabinet and run for re-election to the House of Commons in a snap election called by Jean Chrétien. Chretien appointed his friend the choice and powerful position of Minister of Industry before the election, replacing John Manley, and Tobin was easily elected in the riding of Bonavista—Trinity—Conception. His departure from the premiership caused speculation among Newfoundlanders and Canadians about his aspirations for the leadership of the federal Liberals following what was assumed would be Chrétien's final term as prime minister. Tobin's position in Industry would allow him to develop a relationship with the nation's business leaders who would ultimately be financing any potential leadership campaign. In the winter of 2002, Tobin abruptly resigned both his cabinet portfolio and parliament seat. Observers interpreted that his departure of federal politics was due to his frustration at the stranglehold on the future leadership of the Liberal party by the then Minister of Finance, Paul Martin, and possibly because Chretien had promoted John Manley to Deputy Prime Minister, which designated Manley as the preferred successor.
In retirement from politics, Tobin has served on the board of several Canadian corporations. He became CEO of Magna International Developments (MID), controller of Magna's vast real estate and horse track holdings, the latter through Magna Entertainment Corporation. After only a few months in the position, he left after disagreements with Magna chairman and controlling shareholder Frank Stronach. The dispute was supposedly over the propriety of a share buy-back program, while others suggested that it was because Stronach would not give Tobin autonomy to operate. He is now a Senior Business Advisor with Fraser Milner Casgrain LLP in Toronto and a member of the firm's Public Policy Group. He has authored his suggestively-named auto-biography entitled All In Good Time.
With the defeat of the Liberals in the 2006 Canadian federal election to Stephen Harper's Conservatives, Prime Minister Martin resigned from the leadership of the party. There were frequent rumors that Tobin, and other former cabinet colleagues Allan Rock and John Manley would run to succeed Martin. On January 31, 2006, Tobin officially announced that he would not be running for the federal Liberal leadership.