The state Legislature, dominated by Democrats, rushed to change state law to allow the temporary appointment. Before Kennedy's death, state law did not allow the governor to appoint a replacement and only provided for a special election.
Patrick thanked the Legislature for their swift action to change the law and allow Massachusetts to have two votes in the U.S. Senate. He signed the bill Thursday morning and sent a letter to the Secretary of State that made the appointment immediate.
"The issues before the Congress and the nation are simply too important to Massachusetts for us to be one voice short," he said.
Theoretically, the interim appointment once again gives Senate Democrats a filibuster-proof 60-vote majority that could make it easier for the party to force through President Barack Obama's health insurance reform agenda. However, Democrats have not reached a consensus on health reform. Also, longtime West Virginia Sen. Robert C. Byrd has been absent from the Senate for much of the past year. He remains hospitalized after falling at his home earlier this week.
The Massachusetts succession announcement has special significance because of Kennedy's devotion to the health reform issue. His prolonged illness prevented him from using his full influence or vote during the past months of the heated reform debate.
President Barack Obama praised Kirk as a "distinguished leader" who will carry on Kennedy's work until the special election. "I am pleased that Massachusetts will have its full representation in the United States Senate in the coming months, as important issues such as health care, financial reform and energy will be debated," the president said in a statement.
Kirk said he accepted the appointment as an honor and with humility - and said the temporary appointment was Kennedy's last public wish.
"(Kennedy) often said that representing the people of Commonwealth of Massachusetts was highest honor he could have possibly imagined. It will be my highest honor as well," Kirk said.
Kirk said he plans to retain Kennedy's staff. The 71-year-old attorney is a well-known Democratic Party operator who ran the DNC from 1985 to 1989. He worked as an aide for Kennedy from 1969 to 1977. He is also chairman of the John F. Kennedy Library Foundation.
Kirk will hold the seat temporarily until the state holds a special election on Jan. 19, when voters will chose someone to serve the remaining three years of Kennedy's term. He said he will not run to fill the rest of the term.
Republicans charged that Democrats were too partisan in changing the law. Democrats changed the law in 2004 to prevent the governor from appointing a successor when it was possible that Republican Gov. Mitt Romney could name a replacement if Sen. John Kerry were to become president.
---- By Quinn Bowman, Online NewsHour