Sidhu's wife Navjot Kaur had joined Congress in November last year leading to speculation that he may follow suit.
"Indian National Congress (INC) welcomes S Navjot Singh Sidhu into Congress family and we thank Congress Vice President for his visionary approach in bringing together like-minded people on common platform under the Congress umbrella," Congress spokesperson Randeep Singh Surjewala said in a statement.
"Known for straight taking, ideological commitment to the cause of nationalism as also wit and humour, we are certain that Congress party will be immensely strengthened in Punjab and elsewhere with the entry of Sidhu," said the statement posted on the party twitter handle.
Navjot Kaur along with Pargat Singh, a former Akali Dal legislator who had joined hands with Sidhu to form the outfit Awaaz-E Punjab, had joined Congress after the Sidhus left the BJP.
Earlier, there was speculation that the couple may join Aam Aadmi Party but their talks with AAP leadership failed.
Punjab goes to polls on February 4.